another thing that I just thought of, you are using a group field with sub fields… You can’t update the sub field directly using update_field(). You either have to update the group field with an array of sub fields (field key => value pairs), or you need to use update_sub_field(), https://www.advancedcustomfields.com/resources/update_sub_field/
Yes, a taxonomy field holds and array of term ID as string values.
