Direct posting to partner & is not allowed.

What causes this issue?

You try to perform a partner direct posting. Such a posting is allowed,
only if the partner belongs to the specified venture/equity group. In
the current case, no venture was specified and the system will set the
corporate venture by default. The only valid partner in a corporate
venture is the operator and so posting to partner &V1& is not valid.

System Response

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.