This solution works: ContactManager_to_Yealink_AddressBook no longer able to pull contacts · Issue #25 · sorvani/freepbx-helper-scripts · GitHub
From experimenting, simply slipping $bootstrap_settings['freepbx_auth'] = false; in before pulling in freepbx.conf seems to patch things up just fine,
I’m using it at two sites with Yealinks and it works!