I've been trying to set up a webhook subscription with Printify, but their validation request is consistently failing. I've done extensive debugging and the evidence seems to point towards the request being dropped before it reaches my application container.

GOAL : I'm trying to subscribe to the product:update webhook from Printify. This requires my n8n webhook URL to successfully respond to an initial validation "ping" (POST request) from Printify's servers

The Environment:

• Service: n8n

• Hosting: Railway

• Webhook URL:https://primary-production-2739c.up.railway.app/webhook/product-status

The Problem :

When I try to create the webhook subscription in Printify (via their API), the request fails every time with the error:

400 - "{\"status\":\"error\",\"code\":9004,\"message\":\"Operation failed.\",\"errors\":{\"reason\":\"Webhook validation failed\",\"code\":9004}}

This indicates that Printify's server did not receive a 200 OK response from my URL in a timely manner.

DEBUGGING JOURNEY

• Confirmed the webhook URL is active and accessible by sending request from browser. While I did that, I got the response :

  "Received request for unknown webhook: This webhook is not registered for GET requests."

• Used respond immediately option in n8n to confirm the issue is not with n8n's internal logic for responding

• Analyzed network metrics in railway to conclude that the requests are successfully arriving at my service's network interface on Railway

I would like to know if the POST request from Printify is being dropped or blocked by any intermediary layer within Railway's infrastructure after it's been registered as ingress traffic but before it's forwarded to my application container.