So that’s part of the problem. You can’t update a field that is a sub field or a nested nested field with just the field key for that field. To use just the single field key it must be a top level field. To update a sub field you need to use update_sub_field() https://www.advancedcustomfields.com/resources/update_sub_field/ and supply a selector that is an array that provides a path to the sub field, And I’m going to be honest, I don’t completely understand how this works.
