Verifying source and destination countries If a non-supported country code appears in the incoming data, we recommend that you configure the Project to generate an error message. For example, an email informing the Seller about the non-supported country. In order to automatize the error handling, it is recommended to verify that the source and destination countries are supported by TrustWeaver before the invoices are sent to the TrustWeaver On Demand service for signing and validation. For information about supported countries and country codes according to ISO 3166, see Identifying source and destination countries.