The most likely cause of a transaction being cancelled is for security purposes and are almost always entirely beyond our control. The cancellations are invariably caused by either the donor's a credit card provider (that issued the actual credit or debit card used) or by ammado's payment provider - WorldPay (www.worldpay.com).
Credit card providers, such as Banks, employ security checks such as tracking historical usage of a credit card and will often cancel a transaction that appears inconsistent with a credit card holder's shopping history. If, for example, you have never made a donation online, then this could be a factor for a credit card provider to cancel this transaction. In such cases, a credit card provider may contact you to confirm the transaction or will cancel it outright. You may need to confirm such transactions with your credit card provider to ensure a successful donation.
The second most likely reason is that ammado's payment provider - WorldPay - has cancelled the donation. WorldPay implement a number of security checks in order to protect our nonprofits from receiving fraudulent donations and these checks can sometimes be overly cautious. If you are continuously experiencing cancelled transactions and you are sure it is not caused by your credit card provider, then you may need to either use a different credit or debit card or contact firstname.lastname@example.org and explain the issue.