An Integration Procedure is the preferred solution because the FlexCard must combine data from Salesforce and an external REST API. OmniStudio Integration Procedures are server-side, declarative processes capable of reading Salesforce data, making external REST calls, transforming results, and returning a consolidated response to a FlexCard. A typical architecture is for an Integration Procedure to use a Data Mapper to retrieve a relevant Account value, such as a ZIP code, and then make a REST call to an external weather service for the current or historical conditions associated with that location. Salesforce recommends Integration Procedures as FlexCard data sources when several actions or data sources must be combined because multiple operations can execute in a single server call. This improves flexibility, performance, and maintainability compared with moving orchestration logic to the client. A DataRaptor or Data Mapper Extract alone is appropriate for Salesforce data but does not by itself orchestrate the Salesforce extraction with the external weather service. Custom Apex could perform the work but introduces unnecessary code where OmniStudio provides the required declarative capability. Streaming API addresses event or data streaming rather than this synchronous aggregation requirement.