Don't worry! This can happen for a number of reasons.
First, check your bank account to make sure you have sufficient funds in your account. If you have sufficient funds but are still having an issue try checking the details in your glassons.com account to ensure that the card details such as the start date and card type are correct and your billing address is the same one the card is registered to.
If the problem persists, enter the details of another card and try that.
If you feel you aren't getting anywhere then contact our Customer Service Team on firstname.lastname@example.org who will try to advise you further.