For a matching record in an indirect lookup relationship, what must you select?

In an indirect lookup relationship, selecting a custom field with an External ID is necessary because it serves as the key that matches the records between Salesforce and an external system. This custom field allows Salesforce to reference and correlate external data, enabling it to establish the relationship without requiring a typical direct reference or a standard field.

The External ID field stores a unique identifier from the external system, which is essential for Salesforce to identify the corresponding record within that system. By using this method, Salesforce facilitates integration and ensures data consistency across both platforms, which is crucial in scenarios where external systems are involved.

Using a different type of field, such as a standard field with unique attributes or the External ID standard field alone, would not provide the flexibility needed for indirect relationships. Additionally, relying on a record ID from another system is not sufficient without that custom External ID designation to create the necessary linkage in Salesforce. Therefore, a custom field with an External ID is essential for properly establishing and managing an indirect lookup relationship.