To add the Magento Increment ID or External Reference Number to the template designer:

* Go to Settings -> Template Designer and edit the template you want to add the Increment ID to.

* Drag and drop a "Labels and Variables" control onto the template and double click on the box.

* Paste this code into the box:

EVAL{BEGIN}Replace[[{ExternalReference}], "MAGENTO",""]{END}

In Linnworks, the External Reference Number (Increment ID) is prefixed with "MAGENTO", so we use the Replace expression to remove the prefix, and only the Increment ID will be displayed.