Symptoms
upcp failed to download TIERS release with the following error:
Tried to sync version /etc/cpanel/TIERS.json file but failed: exit level [die] [pid=***] (Failed to download URL 'http://$IP/cpanelsync/TIERS.json.asc'.)
***** FATAL: The version for tier 'release' is not defined!
Description
The issue is generated by the presence of /etc/cpsources.conf file which contain a wrong URL or IP address
Workaround
Remove the /etc/cpsources.conf or properly configure the file
Documentation
Installation Guide - Customize Your Installation