invoice numbers on pdf invoice do not match with order

-- url of the page with the problem -- : shop.justducks.co.uk
-- HikaShop version -- : 3.0.0 BUSINESS
-- Joomla version -- : 3.6.5
-- PHP version -- : 5.6.3
-- Browser(s) name and version -- : All

Installed "AttachInvoice" PDF Plugin and it generates the attachment to the email properly.

However, the ORDER NUMBER in the confirmation email is: JD17-M2F58

The INVOICE NUMBER on the attached PDF is: JD-17-G1K47

The ORDER NUMBER does not appear anywhere on the PDF document.

Please advise resolution to present the same INVOICE NUMBER on the PDF as the ORDER NUMBER on the email/system admin.

Thank you.

Amending Question:

How can we print the System ORDER NUMBER on the PDF to show both ORDER and INVOICE numbers.

Rather confusing to both the customer and admin for referencing numbers.

We would like to display BOTH the ORDER NUMBER and INVOICE NUMBER on the PDF document.

Thank you. We have performed the modification and will test the results.

Regards.