Initiates a specified campaign, marking it as active and beginning the exchanges.
organisation_id (int): The ID of the organisation under which the campaign is registered.campaign_id (int): The unique identifier of the campaign to be started.X-API-Key: API key for user authentication.400 Bad Request: If the campaign cannot be started due to missing or invalid campaign settings.403 Forbidden: If the user making the request does not have the necessary permissions to start the campaign.404 Not Found: The campaign does not belong to the specified organisation.