Use pre-allocated tracking number

If you need to communicate the Royal Mail tracking number to your customers before you have all the shipment details, you can request a pre-allocated tracking number by providing only a few details: Destination Country, Postcode (depending on the Destination Country), Service Code, the Shipping Account that you will be using to create the shipment and the Shipping Location if you have more than one Shipping Location linked to the Shipping Account.

After you have all the shipment details you can call the Royal Mail Create Shipment endpoint using the pre-allocated tracking number.

The Create Shipment request using a pre-allocated tracking number can only have one package and all the information sent when requesting the pre-allocated tracking number must match the information sent in the Create Shipment request.
The pre-allocated tracking number does not expire.