When sending messages through the Conversations API, the participant type must always be one of accessKey, flow, or contact, with accessKey being the most common usage. The value of participantId depends on participantType as shown below:
Participant type
Description
Meaning of participant ID
accessKey
A Bird API access key. This is what you'll commonly use when sending messages through the Conversations API
Access key ID
contact
A Bird contact
Contact ID
flow
A Bird flow
Flow ID
Create message in conversation
post
Sends a message in a conversation. The message content can be comprised of either body or template. Attempting to send as a participant that hasn't been added to the conversation results in an error unless the option addMissingParticipants is set to true. Attempting to send messages in a closed conversation results in an error.
Authorizations
HTTPRequired
Uses the Authorization header: 'AccessKey ' followed by your access key token (e.g., 'Authorization: AccessKey AbCdEfGhIjKlMnOpQrStUvWxYzAbCdEfGhIj')