There’s probably a couple places you can jump in with your add_term_meta() code I would guess, but acf/save_post is probably a really good choice. Do you have reservations about using that?
Sometimes I find it tricky when doing things during the “save” process whether ACF fields are set yet or not… whether to use the Field Key, or whether to use the $POST object… and of course, it all depends on the purpose…
… but my new favourite action hook is: wp_insert_post
… maybe give that one a try if you have troubles with acf/save_post … it works for me every single time when coupled with ACF custom fields.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users
Helping others is a great way to earn karma, gain badges and help ACF development!