SEO Belfast

I’ve spent the last week working on what should be a fairly straightforward booking system using PayPal as the payment provider. I’ve been using the PayPal Sandbox to test the code and I’ve encountered very strange and confusing results.
There doesn’t seem to be any logic to what happens when the payment is completed and I’m returned to the confirmation page.

If I’ve selected ‘UK’ as the country I get a ‘the parameter is incorrect’ and if I select ‘Aruba’ as the country and enter the same details except I enter ‘Not sure’ for the state rather than Antrim then the confirmation page shows the correct message i.e. ‘Thank you for booking’.

If anyone can explain this then I’d be very glad to hear from you. I’ve posted this issue on the pdncommunity forum and am still waiting for a proper explanation.