Mattermost was all set up and working but I had to move it to a new server which meant I could no longer use the default SSL port, which meant I could no longer use LetsEncrypt, so I bought a new SSL certificate.
It works using the browser and the Windows app, but the Android app says
Cannot connect to the server. Please check your server URL and internet connection.
systemctl status mattermost.service gives me
http: TLS handshake error from 192.168.0.143:41342: remote error: tls: unknown certific
I looked through similar issues in this forum and saw that the problem might be intermediate CAs - the certificate came with a ca-bundle file but I wasn’t sure what to do with it.
The SSL provider (Sectigo) doesn’t provide any specific instructions for Mattermost.
Based on the conversations in the forums I tried renaming the bundle to .crt, copying it to
/usr/local/share/ca-certificates and running
sudo update-ca-certificates but it didn’t help.