Custom fields on invoice pdf

Hi guys i’m trialling using Jetpack CRM for my company database, I’ve got everything setup and working but i’m having a problem with the invoicing section.

My customers send me an “order reference” for orders, which I then tally my invoices to, so basically i’ve set a custom field up called “Order Ref” in jetpack settings, and it shows on the pages where I create my invoices. However when I come to pdf an invoice, there’s no sign of this custom field. Ideally i’d like it to show below the invoice date, i’ve fiddled with the html template but I can’t work out what variable to use, the defaults are for example: ###CUSTINFOTABLE###, does anyone know what I can use to display my custom fields?

Many thanks!