Sangoma silently removed the ability to configure XML-API for Yealink ‘T5’ handsets in EPM v15.0.39.39 about a year ago (citing them not being supported, even though they ‘mostly’ worked fine in my experience), maybe they removed this ability for the models your referring to also - Here is a post I made at the time when the change happened (https://community.freepbx.org/t/dialling-from-contacts-phoneapp-on-yealink-t5-series-handsets/73063)