Node Endpoint 403 Fix

My Node-based API has an endpoint that suddenly refuses requests whenever certain query or path parameters are present. The headers and body reach the server just fine, but as soon as those parameters hit the route, the call dies with a 403 Forbidden.

I have confirmed that:
• The problem lies in the request parameters, not the headers or body.
• The failure manifests consistently as a 403 rather than a 400 or silent timeout.
• The same parameters work on a local build, so the issue is likely tied to production middleware, validation, or ACL logic.

What I need from you:
1. Pinpoint the exact check, middleware, or configuration that flags the parameters and triggers the 403.
2. Patch or refactor the offending code (Express router, validation schema, custom guard, or Nginx/Firewall rule) so valid requests pass through.
3. Provide a concise summary of the root cause and the fix so I can avoid regressions.

Tech stack: Node.js 18, Express 4, Joi for validation, and a front-end hitting the API via Axios. Access to the repository and staging server is ready; once the patch is merged and a successful test proves the 403 is gone, the job is complete.