EdwinRookie
Hello,
Luckily this is a very simple process. If you get this message then you have either not filled in your mobile phone number in your profile or you didn't fill in it when you were trying to add the card.
First delete the payment method from the Google wallet, so it doesn't keep going wrong.
Then make sure that your bunq profile has your mobile phone number and once you add the card to the Google wallet make sure to also give up your mobile phone number. If both are correct and the same you will be send a text message to verify your identity.
Hope this helps