This account is defined as the header account of cash pool &1.

What causes this issue?

This bank account is defined as the header account of cash pool &V1& and
now you are trying to define it also as a subaccount of the same cash
pool. However, the system does not allow you to define a bank account as
both the header account and the subaccount of a cash pool.

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?

Specify another cash pool.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.