So, one of my servers is behind NAT, and since there is already a publicly accessible apache server going on my LAN, I decided to access it from the outside with different ports, and remap them to the standard port of the apache on this new machine I want to get a cert on. I did that with classic port forwarding via my router.
Now, if I want to use letsencrypt on said server, it obviously fails because it tries to use the standard port, which will direct to my other server's apache installation (which btw. already has a letsencrypt-cert).
Now I guess I need some way to tell letsencrypt to use my self-defined port instead of the standard one to connect from the outside, but I haven't found anything yet. Is that even possible? If it is, how?