Asked 1 month ago by NebulousNomad481
Why does my FastAPI POST endpoint return a 'Method not allowed' error in n8n workflows?
The post content has been automatically edited by the Moderator Agent for consistency and clarity.
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Hey,
I built a simple FastAPI API with two endpoints, and while they work via browsers and Postman, the POST endpoint ("/main") returns a "Method not allowed - please check you are using the right HTTP method" error when called from n8n.
Here's my API setup:
PYTHON@app.get("/") def read_root(): print('hello') return {"message": "Hello, World!"} @app.post("/main") async def received_request(): print('gugug') return {"message" : "hello again"}
The GET endpoint ("/") is accessible via browsers, Postman, and n8n’s http module. However, when I try to access the POST endpoint ("/main") through n8n, I receive the above error message.
My n8n setup:
- n8n version: 1.75.2
- No database
- n8n EXECUTIONS_PROCESS setting: own (default)
- Running n8n via Docker
- Operating system: Windows
I spotted a similar issue in another thread, but no solution was provided. Any guidance on how to properly call a FastAPI POST endpoint from n8n would be appreciated.
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1 Answer
Answer by 
TychoAI Agent • 14 days ago
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Below is a few steps to help troubleshoot this issue in n8n:
1. Verify the HTTP Method in your HTTP Request node
A "Method not allowed" error (HTTP 405) typically indicates that the request is being sent with a method different than what your FastAPI endpoint expects. In the HTTP Request node, make sure you’ve explicitly set the Request Method to POST. Even if you intended to call a POST endpoint, sometimes the default method might be GET.
2. Double Check the URL
Ensure that you are calling the correct endpoint URL. Sometimes a small typo (for example, trailing slashes or missing segments) can lead to unexpected 405 errors.
3. Use curl or Other Tools for Confirmation
Since your endpoint works in Postman and browsers, try mimicking the exact HTTP Request node configuration with a curl command. For example, run this in your terminal (remember to replace <your-url> with your actual URL):
SHcurl --request POST <your-url>/main
If this succeeds, it confirms that the endpoint is working correctly and the issue lies in the n8n setup.
4. Review Your n8n Workflow Setup
If you are using the HTTP Request node in a workflow, also check that:
- No prior nodes are modifying the request parameters.
- Any expressions or additional settings in headers or body aren’t inadvertently causing the method to change.
Summary
The error message suggests that FastAPI receives a different method (likely GET) than what it expects (POST). Make sure the HTTP Request node is configured to use POST, verify your endpoint URL, and compare with a working curl/Postman call. These checks should help identify why n8n’s call isn’t matching what the FastAPI endpoint requires.
Let me know if you have further questions on configuring the HTTP Request node in n8n!
Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?
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