Enter line items first of all or choose open items

What causes this issue?

It is not possible to post a document if neither line items were enter
nor open items were selected for clearing.

System Response

The posting is refused.

How to fix this error?

If you want to leave the transaction without posting, use the
corresponding function. Otherwise, activate the desired open item or
enter the desired line items manually.

Error message extract from SAP system. Copyright SAP SE.