Hi Jos101,
If you are able to manually send funds to paymentsyxb@scirra.com from your Paypal account and then send me an email at tomyxb@scirra.com I can issue your license manually.
This is the first report I've heard of problems with Paypal which lead me to suspect it's probably not an issue at our end.
If you phone your bank up and ask why the transaction was declined you will get a more detailed reason as to why this happened.
Tom