RPi connection to internet via 4/5G connection

Step by step eh? Sounds like people find themselves on a similar journey with this kind of hardware…

From this post the replied suggests that:

This looks like APN conflict. Check your PDP context → are you using default PDP context e.g. 1 or something else e.g. 3? I faced similar issues and it turned out that there were multiple APNs (default and non default) conflicting resulting in cell provider kicking out the connection (LCP terminated by peer).

THis other troubleshooting resource points to incorrect APN configuration as a reason for spurious hangups too.

Modem hang up and you tried all solution, nothing work and do not know why

I have encountered few time on this problem, it hang up while connecting to network.
Because of incorrect APN, try all APN you can find on network and in your phone’s setting. To change the APN, edit /etc/ppp/peers/provider