How does Nginx get the certificates stored on a remote server?

I have a problem, the reverse proxy server (Nginx Proxy Manager) is located in a private subnet, my reverse proxy does not have Internet to manage the certificates (using Cerbot), the certificates are generated and stored on a remote server in the private subnet and I need the reverse proxy server to get or point to the certificates stored on the remote server

Just to make sure I’m clear, is the issue that the proxy server is not accessible via port 80 on the outside? If that’s the case, have you considered using an API approval such as from Linode, Route 53, or some other service? Usually that’s the way to go, if it fits your layout.

Exactly, this server (Nginx Proxy Manager) is not accessible via port 80 on the outside, because it belongs to a private subnet without internet access due to institutional policy. I have an internal DNS server not accessible from the outside as well. There is also a server that stores all the certificates of the institutions managed by certbot. I have access to the server that stores the certificates via SSH, so my plan is to mount a partition using SSH and tell the reverse proxy server (Nginx Proxy Manager) to take the certificates in the mounted partition, do you think that works?