Problems with "site.webmanifest"

I’m running a Deno/Fresh project. Static files are served fine except site.webmanifest which can be accessed directly but as part of the website. There a couple of requests happen automatically which eventually lead to a CORS fail:

  1. Request to https://9000-idx-…

HTTP/1.1 302 Found
Location: https://80-idx-…

  1. Request to https://80-idx-…

HTTP/1.1 302 Found
Location: https://8282-idx-…

  1. Request to https://8282-idx-…

HTTP/1.1 302 Found
Location: https://9000-idx-…

And this one is marked as CORS error: MissingAllowOriginHeader