Transfer all transaction data to contract account &1

What causes this issue?

For contract account category of contract account &V1&, it has been
specified that only one business partner can be assigned. When you
transfer the contract account to a new business partner, therefore, you
also have to transfer all transaction data also.

System Response

The transfer is not allowed

How to fix this error?

Select all transaction data for the contract account.

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.