Ship Station Packing Ref field include in email

Hi, I have the ShipStation plugin and it passes through the tracking link to a field called: Package Ref (See attached)

I want to include this in my SHIPPING email that goes to the customer. How can I include this in my email code, I can see that it is a custom field so not sure what the variable name is.

I need to include it so my customers can see the tracking code.

Thx