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ERROR 2204: This callback ID is already registered in the delivery report router

This error happens if the mobile operator returns the same callback reference ID for two different messages. It can also happen if you send your messages through a GSM phone or GSM modem and you send several messages to the same phone number over time.

What is the callback reference ID

When the Ozeki software submits an SMS messages to the SMS service provider (Mobile Network Operator), the SMS service provider returns a unique string. This unique string is called the callback reference ID. The callback reference ID is also included in delivery reports returned by the SMS service provider. You receive a delivery report SMS message in case the originally submitted SMS is delivered to the recipient handset.

How are callback reference ID's handled in the Ozeki SMS software

When an SMS message is submitted the callback reference ID is stored in the Ozeki software for the purpose of matching future incoming delivery reports to submitted SMS messages. When a delivery report SMS is received the Ozeki software checks the callback reference ID included in the delivery report SMS to find out which originally submitted message this delivery report belongs to. If the originally submitted message is found it's status is set to delivered and the callback reference ID is deleted from the Ozeki software.

When does Error 2204 happen?

Error 2204 happens if the SMS service provider fails to provide a unique callback reference ID for each submitted message. In this case if an incoming delivery report arrives, there is know way for the Ozeki software to decide which originally submitted envelope it belongs to.

The error can typically happen if a GSM modem is used and several messages are sent to the same phone number. If a message is submitted through a GSM phone or GSM modem, the callback reference ID is made up of the last few digits of the phone number and a number that iterates between 0 and 255.

When can I do about this?

Not much. Simply ignore it.