Hi Klaus, I'm sorry but what you mean with : "I receive a OT-53 in the error-text instead of..." However, when you ask for a delivery notification a common communciation flow will be something like that : 1) Client send : OP 51 type O (submit sms) 2) SMSC response : OP 51 type R (submit sms response) When available.. 3) SMSC send : OP 53 type O (delivery notification) 4) Client send : OP 53 type R (delivery notification response) Regards, Marco Romano