If your transactions at physical stores or ATMs are being declined while your card works fine online, it might be that the chip on your card is blocked, or you’ve made five contactless transactions in a row.
The good news is that it’s easy to fix. First, try making a chip and pin transaction. If that doesn’t work, simply head to the nearest high-street bank ATM, insert your card, select "Other services", and then choose "Unblock Chip/Pin". This should help you out.