Always try to have extra credit on your phone to cover any additional network charges that may apply before you initiate your payment to avoid running out of credit. For example, if your game membership costs 12 USD it might not be enough to just have 12 USD on your phone balance to allow for successful payment. This is because your network operator will often charge you for each message that Surfpin sends you (or you send to Surfpin). Sometimes these charges will be absorbed by your inclusive allowance (if you have any) but mostly they will simply appear as additional charges.