Transaction type '&1': +/- sign does not concur with legacy system

What causes this issue?

You can file for the transaction type whether an incoming or outgoing
payment is involved. The value filed here does not concur with the
legacy system data.

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 change the +/- sign for the transaction type or change the
assignment to the BCA transaction types in the legacy system.

Error message extract from SAP system. Copyright SAP SE.