Funds reservation document not in commitment plan

What causes this issue?

You are attempting to specify a funds reservation as the account
assignment for the document. However, either this funds reservation does
not belong to the commitment plan of the contract or you are using a
contract that does not have a commitment plan.

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?

Either use only funds reservations that are also included in the
commitment plan for the contract or use a different contract.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.