These two fields are non-intuitive when setting up a SIP trunk.
The username name is the name that the “type=USER” entries use. The “authorization” name is the name that you actually use to “log in” to the SIP provider when connecting in the details of the USER section of the configuration.
There are several variations on “username” in the USER section of the SIP Configuration, so you may need to try a few combinations to get the mapping of our entries with what your provider is expecting.
One last wrinkle - these entries are usually associated with providers that are expecting you to connect a phone to their system. Some providers specifically block Asterisk servers from connecting to “single-user” accounts. Check with your provider to find out if they support Asterisk PBX servers on their service.