In Salesforce Commerce Cloud, when a Digital Developer needs to integrate with a REST API that expects parameters to be form encoded, the correct service type to register is HTTP Form. This service type is specifically designed for handling form-encoded data being sent to and from REST APIs. The HTTP Form service type ensures that the parameters are encoded correctly according to the application/x-www-form-urlencoded standard, which is typically used in HTML forms and can be consumed by many REST APIs expecting this format.