When populating fields with an import tool it or script it needs to be an import that understands how ACF fields are saved. It isn’t the field value but another hidden custom field that is a pointer for ACF to understand what type of field it is.
Let’s say that your field name is “field_name”. The database will have 2 entries. The first is your field name with your value and the second will be “_field_name” and the value of this field is the ACF field key for this field. It gets more complex for some types of fields.
