"Error self-signed certificate" all of a sudden

Hey,

since last night, all of a sudden, I am getting certificate errors when trying to access my jitsi host via the API.

Accessing the frontend using Chrome works, the certificate is valid.
I checked the certificate on the server using certbot, it is valid and not expired.

But when trying to access that same domain using Postman or Fetch, I am getting “Error self-signed certificate”. Also, when checking my domain with SSL Labs, it fails, it says “Certificate name mismatch”.

Are there any other certificates besides the one for my domain (“jitsi.mydomain.com”)?
Where else could be config errors? What I don’t get is why this happened all of a sudden, after the install worked for 2 weeks.

Update:

I suspect that the turnserver config is the problem (/usr/share/jitsi-meet-turnserver/jitsi-meet.conf). I have a custom prosody plugin, for which to be able to reach via the API, I had to change the upstream mapping to:

    map $ssl_preread_alpn_protocols $upstream {
        ~\bstun\.turn\b  turn;
        default          web;
    }

I mentioned this already in Nginx Proxy Pass for muc_size working in Browser, but not Postman.

Will keep an eye on this.