Stops recipients of one sequence. With emails, it cancels the active recipients with those addresses: all of them if you have read-write access to the sequence, otherwise only the ones you added. Without emails, it cancels every active recipient you added to this sequence. Cancelled recipients get no further emails and are marked completed. You need access to the sequence; without it the response is still 200 with an empty list. An empty emails array cancels nobody. emails must be an array of strings; any other value returns 400.