Do I have to pay for text messages that are not being delivered?

You are being charged when you get an "OK xxxx" response from the server. This is BudgetSMS then also submitted the message to the operator or supplier and is getting charged to that aswel.
When an "ERR xxxx" response is received, you are not charged.

Got OK response, got charged but message was not delivered

The SMS was not delivered. The reason can be a number of things:

  • Network issues
  • Route blockage
  • Bad reception receiver phone
  • Technical issues
  • Unknown receiver MSISDN
  • MSISDN is barred from receiving SMS
  • Receiving MSISDN is on a do-not-disturb list