SA_TRAN_ITEM "Not Available" when we try to create rule

Hello,

We are trying to create a new audit rule in ReSA where the user cannot leave the "Selling Item" field blank when creating a transaction.

In order to do this, we are adding SA_TRAN_HEAD as a Realm, and then SA_TRAN_ITEM. However, we are unable to add SA_TRAN_ITEM as we get the message Not Available and we can't press OK.

Does anyone know why this is happening?