ITALY EINVOICE - How to get the value of the external value in the value mapping?

Hi，

The company I work for has recently added new tax codes and invoice types.

As an IT personnel, I am responsible for maintaining the GET_NATURA_CODE and GET_DOCUMENT_TYPE_SD in the T-code: /N/AIF/VMAP value mapping.

However, users do not know how to get the external value of tax codes and invoice types, so I would like to ask how to confirm the external value? Are there any rules or official instructions?

Thanks in advance.

Albert