Supplier Payment Terms

I am having issues on posting Supplier Invoices from Syrinx (Point of Rental) Hire Software, to Reckon Accounts Premier Edition 2020. When they migrate to Reckon, the payment terms are not updating, eg, supplier invoice dated 28/01/21 is showing as due 28/01/21 (COD), need for the payments terms to default to Net 30 days EOM -to be due 28/02/21 - I am having to currently manually override them in reckon, which is very cumbersome, I have spoken to Syrinx support and they say its a Reckon issue, please help