Look at your server logs and make sure that POST requests get routed to the lemmy backend, not the frontend. The frontend does not proxy requests to the backend if the frontend doesn't handle it.

Check your NGINX logs and look for POST requests to /inbox as well as /.well-known/webfinger.

You can unsubscribe and subscribe again while tailing the logs to hopefully see the request come in, and make sure it's a 200. If it's a 400 or 404, triple check it's not going to lemmy-ui.

Been there, done that.

Try this script and set it up. It seems to work out the kinks of federation.

New install of a server... typical Docker proxy setting or Nginx.

Make sure your activity pub Is working by using curl to fetch it with the activitypub type. There's instructions on the main Lemmy instance guide.

I see this often using any instance other than the one the community is on. It's because the instances need to talk to each other communicating any changes and also approving them. It will do this automatically, it just takes varying amounts of time depending on the queue and distance from each other.