diff --git a/scripts/generate_resources.py b/scripts/generate_resources.py
index 5a8c46e2..0abb8254 100644
--- a/scripts/generate_resources.py
+++ b/scripts/generate_resources.py
@@ -294,6 +294,7 @@ def generate_method_body(
     body_params = [p for p in params if p["in"] == "body"]
     raw_body_params = [p for p in params if p["in"] == "raw_body"]
     path_params = [p for p in params if p["in"] == "path"]
+    header_params = [p for p in params if p["in"] == "header"]
 
     # Handle path parameters
     path_expr = f'"{path}"'
@@ -314,6 +315,9 @@ def generate_method_body(
     use_query_params = http_method.upper() in ("GET", "DELETE") and query_params
     use_body_params = http_method.upper() in ("POST", "PUT", "PATCH") and body_params
     use_query_on_post = http_method.upper() in ("POST", "PUT", "PATCH") and query_params
+    # Only _get and _post accept a `headers` kwarg (see BaseClient); no
+    # operation on PUT/PATCH/DELETE currently has a header param.
+    use_headers = http_method.upper() in ("GET", "POST") and header_params
 
     # Build params dict if needed
     if use_query_params or use_query_on_post:
@@ -329,12 +333,38 @@ def generate_method_body(
             lines.append(f"            {p['name']}={p['name']},")
         lines.append("        )")
 
+    # Build headers dict if needed. Keyed on original_name, never the snake_case
+    # param name: the wire name is `x-request-id`, and _build_params would have
+    # camelCased it to `xRequestId`.
+    if use_headers:
+        if all(p["required"] for p in header_params):
+            entries = ", ".join(
+                f'"{p["original_name"]}": {p["name"]}' for p in header_params
+            )
+            lines.append(f"        headers = {{{entries}}}")
+        else:
+            lines.append("        headers: dict[str, str] = {}")
+            for p in header_params:
+                if p["required"]:
+                    lines.append(
+                        f'        headers["{p["original_name"]}"] = {p["name"]}'
+                    )
+                else:
+                    lines.append(f"        if {p['name']} is not None:")
+                    lines.append(
+                        f'            headers["{p["original_name"]}"] = {p["name"]}'
+                    )
+
     # Make the request
     if http_method.upper() == "GET":
+        call_args = [path_expr]
         if query_params:
-            lines.append(f"        return {await_prefix}self._client.{client_method}({path_expr}, params=params)")
-        else:
-            lines.append(f"        return {await_prefix}self._client.{client_method}({path_expr})")
+            call_args.append("params=params")
+        if use_headers:
+            call_args.append("headers=headers")
+        lines.append(
+            f"        return {await_prefix}self._client.{client_method}({', '.join(call_args)})"
+        )
     elif http_method.upper() == "DELETE":
         if query_params:
             lines.append(f"        return {await_prefix}self._client.{client_method}({path_expr}, params=params)")
@@ -348,6 +378,8 @@ def generate_method_body(
             call_args.append(f"data={raw_body_params[0]['name']}")
         if query_params:
             call_args.append("params=params")
+        if use_headers:
+            call_args.append("headers=headers")
         lines.append(
             f"        return {await_prefix}self._client.{client_method}({', '.join(call_args)})"
         )
diff --git a/src/late/client/base.py b/src/late/client/base.py
index 9f83a218..e204c699 100644
--- a/src/late/client/base.py
+++ b/src/late/client/base.py
@@ -35,6 +35,22 @@ def _resolve_sdk_version() -> str:
     return "0.0.0+unknown"
 
 
+def _parse_error_body(response: httpx.Response) -> dict[str, Any]:
+    """Best-effort parse of an error response body.
+
+    Returns {} when the body is empty, when it isn't valid JSON (e.g. an
+    HTML 401 from a proxy in front of the API), or when the parsed value
+    isn't a dict.
+    """
+    if not response.content:
+        return {}
+    try:
+        data = response.json()
+    except ValueError:
+        return {}
+    return data if isinstance(data, dict) else {}
+
+
 class BaseClient:
     """
     Base HTTP client supporting both sync and async operations.
@@ -115,17 +131,23 @@ def _handle_response(self, response: httpx.Response) -> dict[str, Any]:
 
         # Handle errors
         if response.status_code == 401:
-            raise LateAuthenticationError("Invalid API key")
+            error_data = _parse_error_body(response)
+            raise LateAuthenticationError(
+                error_data.get("error", "Invalid API key"), details=error_data
+            )
 
         if response.status_code == 403:
-            error_data = response.json() if response.content else {}
+            error_data = _parse_error_body(response)
             raise LateForbiddenError(
-                error_data.get("error", "Access forbidden - check your plan")
+                error_data.get("error", "Access forbidden - check your plan"),
+                details=error_data,
             )
 
         if response.status_code == 404:
-            error_data = response.json() if response.content else {}
-            raise LateNotFoundError(error_data.get("error", "Resource not found"))
+            error_data = _parse_error_body(response)
+            raise LateNotFoundError(
+                error_data.get("error", "Resource not found"), details=error_data
+            )
 
         if response.status_code == 429:
             raise LateRateLimitError(
@@ -136,7 +158,7 @@ def _handle_response(self, response: httpx.Response) -> dict[str, Any]:
             )
 
         if response.status_code >= 400:
-            error_data = response.json() if response.content else {}
+            error_data = _parse_error_body(response)
             # Pass the entire response body through as `details` so callers
             # (and __str__) can surface the field name (`param`), the stable
             # error code (`code`), and platform-specific context. The API
@@ -146,7 +168,7 @@ def _handle_response(self, response: httpx.Response) -> dict[str, Any]:
             raise LateAPIError(
                 message=error_data.get("error", f"HTTP {response.status_code}"),
                 status_code=response.status_code,
-                details=error_data if isinstance(error_data, dict) else None,
+                details=error_data,
             )
 
         # Return parsed JSON or empty dict
@@ -200,10 +222,13 @@ def _get(
         self,
         path: str,
         params: dict[str, Any] | None = None,
+        headers: dict[str, str] | None = None,
     ) -> dict[str, Any]:
         """Make a sync GET request."""
         with self._sync_client() as client:
-            return self._request_with_retry(client, "GET", path, params=params)
+            return self._request_with_retry(
+                client, "GET", path, params=params, headers=headers
+            )
 
     def _post(
         self,
@@ -211,24 +236,27 @@ def _post(
         data: dict[str, Any] | None = None,
         files: dict[str, Any] | list[tuple[str, Any]] | None = None,
         params: dict[str, Any] | None = None,
+        headers: dict[str, str] | None = None,
     ) -> dict[str, Any]:
         """Make a sync POST request."""
         if files:
             # For file uploads, create a fresh client without Content-Type
             # (httpx sets the correct multipart Content-Type automatically)
-            headers = {k: v for k, v in self._headers.items() if k != "Content-Type"}
+            client_headers = {
+                k: v for k, v in self._headers.items() if k != "Content-Type"
+            }
             with httpx.Client(
                 base_url=self.base_url,
-                headers=headers,
+                headers=client_headers,
                 timeout=self.timeout,
             ) as client:
                 return self._request_with_retry(
-                    client, "POST", path, files=files, params=params
+                    client, "POST", path, files=files, params=params, headers=headers
                 )
 
         with self._sync_client() as client:
             return self._request_with_retry(
-                client, "POST", path, json=data, params=params
+                client, "POST", path, json=data, params=params, headers=headers
             )
 
     def _put(
@@ -338,10 +366,13 @@ async def _aget(
         self,
         path: str,
         params: dict[str, Any] | None = None,
+        headers: dict[str, str] | None = None,
     ) -> dict[str, Any]:
         """Make an async GET request."""
         async with self._async_client() as client:
-            return await self._arequest_with_retry(client, "GET", path, params=params)
+            return await self._arequest_with_retry(
+                client, "GET", path, params=params, headers=headers
+            )
 
     async def _apost(
         self,
@@ -349,23 +380,26 @@ async def _apost(
         data: dict[str, Any] | None = None,
         files: dict[str, Any] | list[tuple[str, Any]] | None = None,
         params: dict[str, Any] | None = None,
+        headers: dict[str, str] | None = None,
     ) -> dict[str, Any]:
         """Make an async POST request."""
         if files:
             # For file uploads, create a fresh client without Content-Type
-            headers = {k: v for k, v in self._headers.items() if k != "Content-Type"}
+            client_headers = {
+                k: v for k, v in self._headers.items() if k != "Content-Type"
+            }
             async with httpx.AsyncClient(
                 base_url=self.base_url,
-                headers=headers,
+                headers=client_headers,
                 timeout=self.timeout,
             ) as client:
                 return await self._arequest_with_retry(
-                    client, "POST", path, files=files, params=params
+                    client, "POST", path, files=files, params=params, headers=headers
                 )
 
         async with self._async_client() as client:
             return await self._arequest_with_retry(
-                client, "POST", path, json=data, params=params
+                client, "POST", path, json=data, params=params, headers=headers
             )
 
     async def _aput(
diff --git a/src/late/client/exceptions.py b/src/late/client/exceptions.py
index 25cc29f2..643b5319 100644
--- a/src/late/client/exceptions.py
+++ b/src/late/client/exceptions.py
@@ -52,8 +52,12 @@ def __str__(self) -> str:
 class LateAuthenticationError(LateAPIError):
     """Exception raised for authentication errors (401)."""
 
-    def __init__(self, message: str = "Authentication failed") -> None:
-        super().__init__(message, status_code=401)
+    def __init__(
+        self,
+        message: str = "Authentication failed",
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, status_code=401, details=details)
 
 
 class LateRateLimitError(LateAPIError):
@@ -81,15 +85,23 @@ def __str__(self) -> str:
 class LateNotFoundError(LateAPIError):
     """Exception raised when a resource is not found (404)."""
 
-    def __init__(self, message: str = "Resource not found") -> None:
-        super().__init__(message, status_code=404)
+    def __init__(
+        self,
+        message: str = "Resource not found",
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, status_code=404, details=details)
 
 
 class LateForbiddenError(LateAPIError):
     """Exception raised for forbidden access (403)."""
 
-    def __init__(self, message: str = "Access forbidden") -> None:
-        super().__init__(message, status_code=403)
+    def __init__(
+        self,
+        message: str = "Access forbidden",
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, status_code=403, details=details)
 
 
 class LateValidationError(LateError):
diff --git a/src/late/resources/_generated/ad_campaigns.py b/src/late/resources/_generated/ad_campaigns.py
index ca4ee417..6cfe77ce 100644
--- a/src/late/resources/_generated/ad_campaigns.py
+++ b/src/late/resources/_generated/ad_campaigns.py
@@ -214,7 +214,10 @@ def create_ad_campaign(
             bid_amount=bid_amount,
             roas_average_floor=roas_average_floor,
         )
-        return self._client._post("/v1/ads/campaigns", data=payload)
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
+        return self._client._post("/v1/ads/campaigns", data=payload, headers=headers)
 
     def update_ad_campaign_status(
         self, campaign_id: str, status: str, platform: str
@@ -297,8 +300,11 @@ def duplicate_ad_campaign(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
         return self._client._post(
-            f"/v1/ads/campaigns/{campaign_id}/duplicate", data=payload
+            f"/v1/ads/campaigns/{campaign_id}/duplicate", data=payload, headers=headers
         )
 
     def duplicate_ad_set(
@@ -330,8 +336,11 @@ def duplicate_ad_set(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
         return self._client._post(
-            f"/v1/ads/ad-sets/{ad_set_id}/duplicate", data=payload
+            f"/v1/ads/ad-sets/{ad_set_id}/duplicate", data=payload, headers=headers
         )
 
     def duplicate_ad(
@@ -355,7 +364,12 @@ def duplicate_ad(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
-        return self._client._post(f"/v1/ads/{ad_id}/duplicate", data=payload)
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
+        return self._client._post(
+            f"/v1/ads/{ad_id}/duplicate", data=payload, headers=headers
+        )
 
     def get_ad_set_details(
         self, ad_set_id: str, account_id: str, *, fields: str | None = None
@@ -941,7 +955,12 @@ async def acreate_ad_campaign(
             bid_amount=bid_amount,
             roas_average_floor=roas_average_floor,
         )
-        return await self._client._apost("/v1/ads/campaigns", data=payload)
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
+        return await self._client._apost(
+            "/v1/ads/campaigns", data=payload, headers=headers
+        )
 
     async def aupdate_ad_campaign_status(
         self, campaign_id: str, status: str, platform: str
@@ -1026,8 +1045,11 @@ async def aduplicate_ad_campaign(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
         return await self._client._apost(
-            f"/v1/ads/campaigns/{campaign_id}/duplicate", data=payload
+            f"/v1/ads/campaigns/{campaign_id}/duplicate", data=payload, headers=headers
         )
 
     async def aduplicate_ad_set(
@@ -1059,8 +1081,11 @@ async def aduplicate_ad_set(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
         return await self._client._apost(
-            f"/v1/ads/ad-sets/{ad_set_id}/duplicate", data=payload
+            f"/v1/ads/ad-sets/{ad_set_id}/duplicate", data=payload, headers=headers
         )
 
     async def aduplicate_ad(
@@ -1084,7 +1109,12 @@ async def aduplicate_ad(
             rename_suffix=rename_suffix,
             sync_after=sync_after,
         )
-        return await self._client._apost(f"/v1/ads/{ad_id}/duplicate", data=payload)
+        headers: dict[str, str] = {}
+        if idempotency_key is not None:
+            headers["Idempotency-Key"] = idempotency_key
+        return await self._client._apost(
+            f"/v1/ads/{ad_id}/duplicate", data=payload, headers=headers
+        )
 
     async def aget_ad_set_details(
         self, ad_set_id: str, account_id: str, *, fields: str | None = None
diff --git a/src/late/resources/_generated/connect.py b/src/late/resources/_generated/connect.py
index 9e1295a8..e4c11526 100644
--- a/src/late/resources/_generated/connect.py
+++ b/src/late/resources/_generated/connect.py
@@ -301,7 +301,10 @@ def list_pinterest_boards_for_selection(
             profile_id=profile_id,
             temp_token=temp_token,
         )
-        return self._client._get("/v1/connect/pinterest/select-board", params=params)
+        headers = {"X-Connect-Token": x_connect_token}
+        return self._client._get(
+            "/v1/connect/pinterest/select-board", params=params, headers=headers
+        )
 
     def select_pinterest_board(
         self,
@@ -336,7 +339,10 @@ def list_snapchat_profiles(
             profile_id=profile_id,
             temp_token=temp_token,
         )
-        return self._client._get("/v1/connect/snapchat/select-profile", params=params)
+        headers = {"X-Connect-Token": x_connect_token}
+        return self._client._get(
+            "/v1/connect/snapchat/select-profile", params=params, headers=headers
+        )
 
     def select_snapchat_profile(
         self,
@@ -360,7 +366,12 @@ def select_snapchat_profile(
             expires_in=expires_in,
             redirect_url=redirect_url,
         )
-        return self._client._post("/v1/connect/snapchat/select-profile", data=payload)
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
+        return self._client._post(
+            "/v1/connect/snapchat/select-profile", data=payload, headers=headers
+        )
 
     def connect_bluesky_credentials(
         self,
@@ -423,8 +434,11 @@ def list_whats_app_phone_numbers(
             profile_id=profile_id,
             temp_token=temp_token,
         )
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
         return self._client._get(
-            "/v1/connect/whatsapp/select-phone-number", params=params
+            "/v1/connect/whatsapp/select-phone-number", params=params, headers=headers
         )
 
     def complete_whats_app_phone_selection(
@@ -447,8 +461,11 @@ def complete_whats_app_phone_selection(
             user_profile=user_profile,
             redirect_url=redirect_url,
         )
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
         return self._client._post(
-            "/v1/connect/whatsapp/select-phone-number", data=payload
+            "/v1/connect/whatsapp/select-phone-number", data=payload, headers=headers
         )
 
     def connect_whats_app_embedded_signup(
@@ -1002,8 +1019,9 @@ async def alist_pinterest_boards_for_selection(
             profile_id=profile_id,
             temp_token=temp_token,
         )
+        headers = {"X-Connect-Token": x_connect_token}
         return await self._client._aget(
-            "/v1/connect/pinterest/select-board", params=params
+            "/v1/connect/pinterest/select-board", params=params, headers=headers
         )
 
     async def aselect_pinterest_board(
@@ -1041,8 +1059,9 @@ async def alist_snapchat_profiles(
             profile_id=profile_id,
             temp_token=temp_token,
         )
+        headers = {"X-Connect-Token": x_connect_token}
         return await self._client._aget(
-            "/v1/connect/snapchat/select-profile", params=params
+            "/v1/connect/snapchat/select-profile", params=params, headers=headers
         )
 
     async def aselect_snapchat_profile(
@@ -1067,8 +1086,11 @@ async def aselect_snapchat_profile(
             expires_in=expires_in,
             redirect_url=redirect_url,
         )
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
         return await self._client._apost(
-            "/v1/connect/snapchat/select-profile", data=payload
+            "/v1/connect/snapchat/select-profile", data=payload, headers=headers
         )
 
     async def aconnect_bluesky_credentials(
@@ -1138,8 +1160,11 @@ async def alist_whats_app_phone_numbers(
             profile_id=profile_id,
             temp_token=temp_token,
         )
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
         return await self._client._aget(
-            "/v1/connect/whatsapp/select-phone-number", params=params
+            "/v1/connect/whatsapp/select-phone-number", params=params, headers=headers
         )
 
     async def acomplete_whats_app_phone_selection(
@@ -1162,8 +1187,11 @@ async def acomplete_whats_app_phone_selection(
             user_profile=user_profile,
             redirect_url=redirect_url,
         )
+        headers: dict[str, str] = {}
+        if x_connect_token is not None:
+            headers["X-Connect-Token"] = x_connect_token
         return await self._client._apost(
-            "/v1/connect/whatsapp/select-phone-number", data=payload
+            "/v1/connect/whatsapp/select-phone-number", data=payload, headers=headers
         )
 
     async def aconnect_whats_app_embedded_signup(
diff --git a/src/late/resources/_generated/phone_numbers.py b/src/late/resources/_generated/phone_numbers.py
index d7694650..3fdd0a38 100644
--- a/src/late/resources/_generated/phone_numbers.py
+++ b/src/late/resources/_generated/phone_numbers.py
@@ -209,7 +209,10 @@ def view_phone_number_kyc_document(self, document_id: str) -> dict[str, Any]:
 
     def upload_phone_number_kyc_document(self, x_filename: str) -> dict[str, Any]:
         """Upload a KYC document"""
-        return self._client._post("/v1/phone-numbers/kyc/upload-document")
+        headers = {"X-Filename": x_filename}
+        return self._client._post(
+            "/v1/phone-numbers/kyc/upload-document", headers=headers
+        )
 
     def validate_phone_number_kyc_address(
         self,
@@ -543,7 +546,10 @@ async def aupload_phone_number_kyc_document(
         self, x_filename: str
     ) -> dict[str, Any]:
         """Upload a KYC document (async)"""
-        return await self._client._apost("/v1/phone-numbers/kyc/upload-document")
+        headers = {"X-Filename": x_filename}
+        return await self._client._apost(
+            "/v1/phone-numbers/kyc/upload-document", headers=headers
+        )
 
     async def avalidate_phone_number_kyc_address(
         self,
diff --git a/src/late/resources/_generated/posts.py b/src/late/resources/_generated/posts.py
index 6abd2764..f331ea77 100644
--- a/src/late/resources/_generated/posts.py
+++ b/src/late/resources/_generated/posts.py
@@ -154,7 +154,10 @@ def create_post(
             queued_from_profile=queued_from_profile,
             queue_id=queue_id,
         )
-        return self._client._post("/v1/posts", data=payload)
+        headers: dict[str, str] = {}
+        if x_request_id is not None:
+            headers["x-request-id"] = x_request_id
+        return self._client._post("/v1/posts", data=payload, headers=headers)
 
     def get_post(self, post_id: str) -> dict[str, Any]:
         """Get post"""
@@ -359,7 +362,10 @@ async def acreate_post(
             queued_from_profile=queued_from_profile,
             queue_id=queue_id,
         )
-        return await self._client._apost("/v1/posts", data=payload)
+        headers: dict[str, str] = {}
+        if x_request_id is not None:
+            headers["x-request-id"] = x_request_id
+        return await self._client._apost("/v1/posts", data=payload, headers=headers)
 
     async def aget_post(self, post_id: str) -> dict[str, Any]:
         """Get post (async)"""
diff --git a/src/late/resources/_generated/whatsapp_phone_numbers.py b/src/late/resources/_generated/whatsapp_phone_numbers.py
index c3d32894..10795c8d 100644
--- a/src/late/resources/_generated/whatsapp_phone_numbers.py
+++ b/src/late/resources/_generated/whatsapp_phone_numbers.py
@@ -192,7 +192,10 @@ def submit_whats_app_number_kyc(
 
     def upload_whats_app_number_kyc_document(self, x_filename: str) -> dict[str, Any]:
         """Upload a KYC document"""
-        return self._client._post("/v1/whatsapp/phone-numbers/kyc/upload-document")
+        headers = {"X-Filename": x_filename}
+        return self._client._post(
+            "/v1/whatsapp/phone-numbers/kyc/upload-document", headers=headers
+        )
 
     def validate_whats_app_number_kyc_address(
         self,
@@ -402,8 +405,9 @@ async def aupload_whats_app_number_kyc_document(
         self, x_filename: str
     ) -> dict[str, Any]:
         """Upload a KYC document (async)"""
+        headers = {"X-Filename": x_filename}
         return await self._client._apost(
-            "/v1/whatsapp/phone-numbers/kyc/upload-document"
+            "/v1/whatsapp/phone-numbers/kyc/upload-document", headers=headers
         )
 
     async def avalidate_whats_app_number_kyc_address(