You cannot clear down payments for DP chains with other documents

What causes this issue?

You are trying to clear a down payment belonging to a down payment
chain, with another document, for example a down payment request or
invoice.
You can only clear a down payment with another down payment. Such down
payments must belong to the same down payment chain.

System Response

Processing was cancelled.

How to fix this error?

Only select down payments. Note that all down payments that you want to
clear must belong to the same down payment chain.

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.