What software is running on port 443 now? If it’s a Web server like NGiNX or apache I would consider a reverse proxy, so it looks as if Azurecast is running on port 443 as well, even though it’s just the Web server passing data to and from Azurecast.
9 out of 10 times using custom ports is a pain. Recommendation is to not do it.
If you must do it, for this particular problem you could probably:
Stop whatever is listening on port 443
Configure Azurecast to use port 443
Request a new cert for Azurecast
Start whatever was listening on port 443 before
Configure Azurecast to use the original port again
Once the cert has been obtained it doesn’t matter at what port Azurecast runs, but to obtain the cert it looks like it should run on port 443.
Essentially, take both the proxy manager and Azuracast containers offline, comment out the custom HTTP and HTTPS ports within .env in /var/azuracast and then spin Azuracast back up. Go to system administration and press “generate/renew,” and assuming no error messages, you’re good. Spin down Azuracast, edit the .env back to how it was set up previously, and then you can spin it and the proxy manager back up.