fix: handle provider_config type error in passthrough error handler (#12101)

- Fix type error where _handle_error was called with provider_config=None
- Add proper provider config retrieval logic similar to llm_passthrough_route
- Handle cases where provider config may not be available
- Ensure type safety while maintaining backward compatibility

litellm/passthrough/main.py

@@ -86,9 +86,39 @@ async def allm_passthrough_route(
             response = init_response
         return response
     except Exception as e:
+        # For passthrough routes, we need to get the provider config to properly handle errors
+        from litellm.types.utils import LlmProviders
+        from litellm.utils import ProviderConfigManager
+        
+        # Get the provider using the same logic as llm_passthrough_route
+        _, resolved_custom_llm_provider, _, _ = get_llm_provider(
+            model=model,
+            custom_llm_provider=custom_llm_provider,
+            api_base=api_base,
+            api_key=api_key,
+        )
+        
+        # Get provider config if available
+        provider_config = None
+        if resolved_custom_llm_provider:
+            try:
+                provider_config = cast(
+                    Optional["BasePassthroughConfig"], kwargs.get("provider_config")
+                ) or ProviderConfigManager.get_provider_passthrough_config(
+                    provider=LlmProviders(resolved_custom_llm_provider),
+                    model=model,
+                )
+            except Exception:
+                # If we can't get provider config, pass None
+                pass
+        
+        if provider_config is None:
+            # If no provider config available, raise the original exception
+            raise e
+        
         raise base_llm_http_handler._handle_error(
             e=e,
-            provider_config=None,
+            provider_config=provider_config,
         )