Idempotency
Send an Idempotency-Key header on any send. If you retry with the same key, you get the original message back and nothing is sent twice.
cURL
curl https://api.mittis.ai/v1/messages \ -H "Authorization: Bearer $MITTIS_KEY" \ -H "Idempotency-Key: appt-4821-reminder" \ -d '{"from":"+18045550142","to":"+18045550199","body":"See you at 2."}'