Offloading media external server

As some of yall know, 1 of the things I do is website hosting. I got a note from my data center the other day that 1 of my clients had too many files. My thought was perhaps to offload his media to an external server, but, thus far, I haven’t had much success setting that up.

Running WordPress 5.42, Lightspeed on the 1 server & Nginx on the other. Proposed media server is Ubuntu 20.04, the shared hosting is CLOUDLINUX 7.8. PHP is 7.2.

I have a subdomain working on the external server, but WP doesn’t seem to like a media library there, ie, I cannot, for example, add a file to the media library as it never appears. My directories are set to have the owner as www-data, & 0755 permissions for directories & 0644 for files. I did go into the all options screen & set the upload url path to the subdomain on the external server.

Has anyone ever set anything like this up? Conversely, any other ideas as to how to offload these files in order to make my data center happy? BTW, I can successfully ssh/sftp to the subdomain to upload files, I just can’t add them via media library.

Any suggestions very much appreciated. Please stay well & safe.