I’ve noticed the “assigned_user_id” gets NULL value when creating a new invoice. The field is declared as fillable property but it does not get populated when storing the invoice details. Does this field has been deprecated on v5? If not, will there be a chance this field be used for a specific purpose?
When an invoice is created the created by field is automatically set, You can optional set the assigned to field if you want to set a specific user for the record.