There’s got to be a problem in your trunk definition. It could be an IP address error, a bad password, or a bad user ID. Have you tried using the units in “peer” mode instead of “friend” or “user” mode (so the authentication will be exclusively by IP address?
A SIP debug might be in order so you can see what the ATA is actually doing.
Not familiar with that specific device, but other Cisco devices have a 30 character limit on passwords. FreePBX generates 32 character passwords by default but that is adjustable in Advanced Settings.
I had a similar experience with an old LeadTek BVA8051 ATA I picked up at the thrift store (new in the box) - I struggled for several hours trying to get it to authenticate, only to discover it had a 20 character limit on the SIP password.