Bad gateway in Remix app


I’ve deployed a Remix webservice, but I keep getting a bad gateway error from the healthcheck.
This web service worked perfectly fine when it was in the free tier. From what I’ve seen elsewhere, the problem seems to be that Render suddenly cannot listen to localhost. So, my hypothesis is that I need to change the host to, however, setting the HOST env variable does not seem to help.

Anybody who has some experience with this?