External API activity will show the format of the request body JSON format that will be generated on the Inbound Mapping tab of the activity, under Post Body Template. This format is also shown in the documentation - https://docs.adobe.com/content/help/en/campaign-standard/using/managing-processes-and-data/data-management-activities/external-api.html#description The request body format is not customizable at this time. Hope this helps.