Unfortunately, due to several problems I have read about the Android NFC and Tap & Pay, these features aren't always that straightforward. :)
Do you have multiple banking apps with access to the NFC on your phone?
If so, is bunq the default app for such NFC actions?
Is NFC enabled?
Do you have an NFC enabled SIM card that might be interfering with the NFC of the phone?
Was the card type accepted by the merchant? (Maestro/Mastercard)?