API reference · Messages
Send a direct message
POST /v1/conversations/{id}/messages
Free: messaging never spends credits.
Request
Authenticate with a bearer API key. Agents calling over MCP authorise with OAuth instead and never handle the key.
curl -X POST https://api.postlake.dev/v1/conversations/{id}/messages \
-H "Authorization: Bearer $POSTLAKE_API_KEY" \
-H "Content-Type: application/json" \
-d '{"account":"…","text":"…","humanAgent":true}'Parameters
| Field | Type | Required | What it is |
|---|---|---|---|
id | string | Yes | In the URL. |
Body
| Field | Type | Required | What it is |
|---|---|---|---|
account | string | Yes | |
text | string | Yes | |
humanAgent | boolean | No | Assert that a PERSON wrote this reply. Meta allows a reply within 24 hours of someone's last message; the Human Agent tag extends that to 7 days and is granted only for replies a human composed. Never set it for an automated reply: the account carries the penalty, not the caller. |
Response
Sent (200).
Example
"…"Limits
Write operations are limited per account, and every response carries X-RateLimit-Remaining and X-RateLimit-Reset. A 429 includes Retry-After. Send an Idempotency-Key so a retry after a timeout cannot duplicate the work.
Calling this from an agent
Agents do not call REST. They call tools. Over the hosted MCP server this operation is list_conversations, and the agent authorises with OAuth so your API key is never pasted into a chat or seen by the model. The reply comes back in the same normalised shape you see above, which is what lets an agent reason about it without a per-network branch.
You control what any one agent may do with it: which brands it may act for, which networks it may reach, how much it may do in a day, and whether it may spend credits you bought up front. See the MCP server.
Errors
Every failure uses one shape: a stable type, a granular code, the field at fault in param, and a plain-language fix. An agent can act on it without a person reading the message. See Errors and retries.
Idempotency-Key and a call that already succeeded returns its original result rather than repeating it.Common questions
Can an AI agent do this without the REST API?
Yes. Over MCP the same job is the list_conversations tool. The agent authorises with OAuth, so no API key is pasted into a chat or seen by the model, and the answer comes back in the same normalised shape.
Is it safe to retry this call?
Yes. Send the same Idempotency-Key and a call that already succeeded returns its original result instead of repeating the work. That is what makes it safe to hand to an agent that retries on its own.
What happens when it fails?
You get one error shape: a stable type, a granular code you can branch on, the offending field in param, and a fix written so an agent can correct itself rather than stop. Full list on Errors and retries.