For successfully syncronizing Unity Connection 12.5.x to PCP you need to create a “proxy user” from the Unity Connection CLI.

Go to Unity COnnection CLI and enter the following:

utils cuc proxy usrcreate 
utils cuc proxy usrpasswd
utils cuc proxy enable

Use this new User in Prime

After that you are able to successfully sync the Unity Connection Server

https://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/collaboration/12-6-SU1/provisioning/Guide/cpco_b_prime-collaboration-provisioning-12-6SU1/cpco_b_prime-collaboration-provisioning-12-7_chapter_011.html#task_41743B408DE04AB8B97024DE874BD687