Buyers ship service does not match what shows on print label detail

[kaki8379]

Buyer selected ups ground  as ship service and paid. When I go to print the label, usps flat rate envelope appears. I cannot edit the ship service to ups. The buyer has an address with a P.O. Box in their address, could that be the issue and will the buyer be able to change the address after they paid?  Thanks for your help!

[rfmtm · Accepted solution]

Buyer has to change address before they pay.  But you can always ask if shipping USPS is ok, if already paid.