I tried to do this, but it won’t show up.
1) https://ibb.co/mNy3QD9 (it works, it adds correctly to array)
2) see here dump of $field_group https://ibb.co/wsL8dss
3) it even correctly shows up when editing ACF https://ibb.co/DC7ZYPh
But when I am in product, fields won’t show up. Any guess what’s wrong?