It may be that the card was not held correctly against the reader. Try again, holding it still in front of the validator.
If the problem continues, possible reasons are:
• The card is not accepted
• Insufficient balance
• Card expired
• Card not contactless
• Card temporarily blocked
In these cases, contact your bank to check.
TIPS: If you are using a digital wallet on a smartphone or smartwatch, try paying with the physical card.