Q:

Booking canceled for Hotel xy in Barcelona

Just received a message in my inbox from booking.com
This reservation was canceled because of an invalid credit card.

Dear JH,
Your reservation at Hotel XY is now canceled. You don’t need to do anything else, but if you have questions for the property, feel free to contact them at ......

Why?
Reservation was confirmed 7 days ago. I have used my VISA electron card. Should I email booking.com? Can they charge me again even if my hotel booking was cancelled?

A:

It looks like you used a debit card instead of a credit card and that the account the card is for also had not enough money at the time they tried to take money out of the account.
For a hotel, and the booking site, it comes up as an invalid (for the purpose) card and that is a big bad sign.
If they keep the room for you and you fail to show up, they are out of the money for the room and have an empty room which they most likely are unable to fill on the night.
As the booking site has send you a message you have not paid, your room booking is cancelled and you will not be charged later, you do not have to do anything. But if not completely sure, contact the booking site or the hotel and make sure. 
If you still want that room, you will need to book it again. If there is no 'pay at the hotel' and a 'without a credit card' option, you best pay the hotel when you book. If the booking site does not allow for the option, ask the hotel.
It is very unlikely they will trust your promise if your card has already bounced.
It will likely be better to book with a credit card and not a debit card. The difference is that a credit card has a guarantied credit and it is much less likely to be 'out of credit'.
And it helps if you keep the card for only booking ahead of time and not use it as a loan or cash source as some people seem to do.

