Terms of payment in PO & differ from those entered

What causes this issue?

You entered the terms of payment indicated on the invoice. Other terms
of payment were, however, specified in purchase order &V1&.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

IF &V2& NE ' '.
Terms of payment key &V2&
ENDIF.
1. Cash discount period &V3& days &V4&%

System Response

How to fix this error?

Check the terms of payment entered and the purchase order number, if
necessary.
To copy the terms of payment from the purchase order, delete your
entries in the <LS>Payment terms</> section and press ENTER.
The system will then suggest the terms relevant terms of payment.

Error message extract from SAP system. Copyright SAP SE.