Item &2 / &3 of installment plan &1 not transfer posted

What causes this issue?

The item &V2& / &V3& from installment plan &V1& is to be transfer
posted although other open installment plan items exist. This is not
permitted.

System Response

The affected installment plan item is not transfer posted.

How to fix this error?

Select all open installment plan items.

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.