The "Use elevated privileges" in UNIX tab of the Target Account triggers to fail the change password.
Also, what is each item of the Privilege Elevation settings mean in the target account >> UNIX tab that is UNIX target application connector?
Privileged Access Manager, all versions
Check the account can run the passwd command via accessing the target server by emulator. If the account does not have the permission about that, it should fail to change the password. After giving an appropriate permission to the account and complete to check if it works, try to change the password via PAM.
Account with UNIX target connector target application >> UNIX tab >> Privilege Elevation: