Transaction &1/&2: Some flows have not been released for posting

What causes this issue?

All the flows in this transaction that have the same payment date need
to be posted at the same time. However, there are flows for the relevant
payment date that have not yet been released for posting.

System Response

The system cannot post the transaction flows.

How to fix this error?

Release all the transaction flows for the relevant payment date so that
they can be posted.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.