Invoice(s) for this line already released

What causes this issue?

The cursor is positioned on a line for released invoice(s).

How to fix this error?

Check whether the cursor is positioned on the correct document or
correct supplier.
If so, release has already been effected. No further processing is
required.
If not, position the cursor on the correct line and then choose <LS>Save
release</>.

Error message extract from SAP system. Copyright SAP SE.