For suppliers, there is a setting on the invoice tab.  Have you checked there?  As explained in help

“Automatic Payment Authorization:
At Final Posting: This is used if all payment plan lines in the invoice should be automatically authorized at the time the invoice is saved with the Finally Posted status. By default this will be reflected in the Supplier Invoice Entry window.

When Posted: This is used if all the payment plan lines in the invoice should be automatically authorized at the time the invoice is Posted when the supplier invoice is in either PrelPosted or Finally Posted state. By default this will be reflected in the Manual Supplier Invoice window.

No: This is used if all payment plan lines in the invoice should not be automatically authorized. By default this will be reflected in the Manual Supplier Invoice window.”

I hope this helps.

Best-

If my understanding is correct, this is would relate to authorising invoice for payment after being finally posted.

Our issue at moment is before finally posting, when the PO value matches the invoice value, but we have to manually add in the authoriser name rather that it pulling through automatically?

Hello,

if I understand your problem right, system is not able to assign authorizers automatically. Please check Authorizer Assigning Rules setup.