What causes this issue?

You have attempted to switch to the business partner system with
<LS><PF>Display</></> or <LS><PF>Amend</></> from the <LS>Payment
Card</> field - but you had not selected a partner or a payment card.

System Response

Select a partner or a payment card and then branch to the business
partner system with <LS><PF>Display</></> or <PF>Amend</>.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.