If you have sent your payment from a custodial exchange, wallet or other 3rd party platform, sometimes they may charge you an additional withdrawal fee which is automatically deducted from the amount you send. This results in your payment being made for less than the amount required on the invoice, causing a partial payment which may delay delivery of your refill or gift card.
To avoid this problem in the future, send your payment to a Bitrefill account, and after one confirmation purchase instantly by paying from there without any amount error.
Or pay from a wallet to which you hold the private keys, and self custody your own Bitcoin. This way you only pay standard network fees, without additional withdrawal fees.