Signal message successfully sent but HTTP 504 timeout from proxy afterwards

[Qhilm]

This is successfully sending a signal message:
curl -X POST -H "Content-Type: application/json" 'https://reverseproxy.home.com:34199/v2/send' -d '{"message": "Test via Signal API!", "number": "+4123123123", "recipients": [ "+4123123123" ]}'

But it seems curl is unable to get the response from the docker container, it hangs for a while and after a timeout shows "Sorry, the page you are looking for is not found" HTML page from my reverse proxy, with a HTTP 504.

After reading #570 I tried setting SWAGGER_HOST to reverseproxy.home.com:34199 but that didn't help.

Any idea? I'm running in native mode.