Purchase Order Reference not showing on invoice

hello all,
I am using one of the templates for the invoices, but when I convert an estimate to an invoice, the PO reference is not showing on the invoice - this is causing many organisation to push back on the invoice saying they need to match the Purchase order reference in order to make payment. I am currently using Jelly and Ice cream template and only the invoice - only the invoice date, issue date and invoice number are appearing - can any one please help on how to solve this problem.

If you go into the Sales menu and then Invoice Customisation, click on the labels box within the preview (highlighted green on the screenshot below) and you will see a list of optional parameters that you can display. Just make sure Purchase Reference is checked, it should then appear.