Hi, @DNAScanner. I also wanted to mention that there is a workaround. You can always put a proxy or load balancer in front of that API so that it does respond on port 443.
Note, that isn’t something Netlify can do so you would need to use some other service. For example, you can put Cloudflare in front of your API. There instructions on this can be found here:
https://developers.cloudflare.com/fundamentals/get-started/reference/network-ports/
The API is still really using post 3000 behind the proxy. However, it will use port 443 via the proxy. You can then proxy the Netlify site to the Cloudflare proxy URL as it will be on port 443 there.
Again, that is a third-party workaround and not a “pure Netlify” solution. However, it might solve this more quickly than a feature request.