Guest Checkout Address Dropdown

[AliceMB]

Hello,

I've sent a payment request to a client without a paypal account. Usually it's possible to select their country (US) from the dropdown box and the address format changes to the appropriate one for the US. However, the most recent time it hasn't changed and stays on the UK address format the whole time and won't accept US address details. What's going on? Can anyone help? 

Thanks