Let's Encrypt SSL Certificate

How would I configure Mattermost to use the Let’sEncrypt SSL Certificate that has already been issued for my server?

Also how would I set Mattermost to use the https port (443) cause everytime I attempt restart Mattermost it doesn’t and it says in a journalctl -xe output

“Cannot bind to port 443: Port already being used.”

It sounds like you might already have a web server configured on that server, which gives you two options.

First, you can modify your web server configuration to act as a proxy in front of Mattermost. This has the advantage of less work - just have to point the server at the Mattermost instance - and the added features of using a proxy to filter traffic or load balance between separate instances.

The second option is to disable your web server. To figure out which server is using port 443 you can run this command:

$ lsof -i | grep 443

Make sure to disable that server, and then you can run Mattermost on port 443.