If you reserve tickets and pay online with Bancontact, iDeal, Visa or Mastercard, there is no need to worry. Your payment is processed immediately and you will receive your e-tickets within 30 minutes.
If something did go wrong, you can always check the status of your active order in your account. If the order was successful, you will also find a link to your e-tickets there. You can also ask for information at the box office at the venue with proof of payment and/or your reservation number. Tickets can always be printed for you free of charge at the box office.