If you pay with your associated debit/credit card through PayPal, then the shop can deny the transaction, if they don't accept that kind of card. PayPal somehow passes this information to the shop with the transaction.
One solution for this is to top up your PayPal balance, and pay with that. However with this method you need to use the exchange rates of PayPal, which are not so good.
Another possibility is to use another type of card, that the shop accepts.
If you don't have any other kind of card currently, then you can generate a virtual card for free on Revolut, that can be used everywhere. This is actually the method I use for all my figure shopping. The balance on Revolut can be topped up paying with your current card, using the exchange rates of your bank, which probably are better than PayPal's.