This could be due to a variety of reasons:

Please ensure the prepaid card is activated.

If the problem persists then please call the card provider on 0203 409 4432.

Please also note:

If you are purchasing items in-store, you can make up to 8 transactions in a day before a PIN will be required.

If the card isn’t working, it might be because the item is considered ineligible for purchase under the card usage terms.

If you return to a website to purchase more items, please ensure the personal details you enter are the same as the first time. Otherwise, the retailer may think the card is being used fraudulently and you may be blocked from using it on their website.