There are various reasons why a recent purchase may not immediately show up in your account. Delays are often caused by your and the seller's banks operating on slightly different time frames, or by minor technical issues which are almost always quickly dealt with.
Usually, it is nothing to worry about. Bear in mind that even though the payment seems instant, behind the scenes, it can take more than 24 hours for your bank to fully process the transaction and to complete the debit process
Banks call these types of instant transactions 'memo posts' or 'pending' transactions. Although a payment record is on your account, your bank has not transferred the money to the seller yet.
Instead, it keeps the funds 'pending' until the seller has checked that your details are correct and you have enough funds to cover the purchase. Even after making the purchase, you may see a pending charge, which will post later. How long this takes will depend on the merchant.
So the bottom line is that if a debit card transaction is not showing up, don't stress! Banks are pretty good at their jobs. More often than not, the funds associated with the purchase you made will eventually be taken from your account. No merchant will decide not to charge you for a product or service, so be rest assured that regardless of how long it takes, provided all is well with the payment, it will eventually show up in your account.
And, in the unlikely event that a payment you made fails to show after several days, don't hesitate to contact the seller or your us to look into it for you.