Hi Kimi,
Alright, now i understand. Thanks for clarifying customer has selected Puerto Rico as state.
I think the problem lays within the TA application we use, Shipmondo, the order was not able to completed booking unless I made change in delivery country to Puerto Rico. They seams not to consider Puerto Rico as part of US. We hade same issue with Aland. They rule under Finlands flag but are is being treated as export nation. Requires custom documentation to send to Aland.
I will check further with Shipmondo to see if they can update their system. Also give them some education on geographic 
Thanks!