Can you clarify which types of failures will use credits and which will not?

So far I have noticed that 'InvalidNumber' uses a credit.

Result code:
1 - OK
2 - NoUsername
3 - NoPassword
4 - NoTo
5 - NoText
6 - LoginInvalid
7 - InsufficientCredit
8 - GatewayError
9 - InternalError
10 - HTTPConnectionError
11 - InvalidNumber
12 - InvalidRequest
13 - ServerTooBusy
14 - MsgIdInvalid

Only one return value will use credits:

1 - OK

All other return values will not use credits

If you believe you have been charged when the result code 11 when submitting a message please email details to support@intellisoftware.co.uk (include username and mobile phone number you was sending to)