Handle TextGrid SMS delivery status callback
Status callback called by TextGrid for delivered/undelivered messages. Updates the corresponding Message document and broadcasts a socket event to the organization.
Body
TextGrid delivery status callback. Only delivered and undelivered are sent.
TextGrid message identifier whose status is being reported.
Twilio-compatible alias of MessageSid; usually identical.
Delivery state: delivered or undelivered.
Tether-provisioned TextGrid number the message was sent from.
Recipient phone number for the outbound message.
TextGrid error code when delivery failed.
Human-readable error description paired with ErrorCode.
Response
Plain-text acknowledgement (TextGrid only checks 2xx).
The response is of type string.
"OK"