External details pushbutton SYSTEM ERROR - PF status &

What causes this issue?

Although the <ZK>External details</> pushbutton was selected, the
logic has determined an invalid PF key status.

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

How to fix this error?

Note the steps you carried out that caused this error and contact your
system administrator.

Error message extract from SAP system. Copyright SAP SE.