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Each API key has two independent buckets of 60 requests per minute, against a sliding window:
  • General — reads, tags, mailbox, notes, files.
  • Messages — sends under conversation.messages.* (text, quick-reply, template).
Saturating one doesn’t affect the other: you can exhaust the messages bucket and keep reading conversations (and vice versa).

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When exceeded

Past the limit the API responds 429 with code RATE_LIMIT_EXCEEDED:

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Response headers

Every 429 response includes these headers:
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Retry-After
integer
Seconds to wait before retrying.
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X-RateLimit-Limit
integer
The limit of the bucket that applied to the request (60 in either one).
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X-RateLimit-Remaining
integer
Requests available in the current window of the bucket that applied.
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X-RateLimit-Reset
integer
The moment the window resets.

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How to handle a 429

1

Detect the status

Treat any 429 response as a rate limit, without parsing the body.
2

Read the Retry-After

Wait the number of seconds indicated by the Retry-After header.
3

Retry with backoff

Resend the request. For large workloads (campaigns), space out the requests instead of sending them in a burst.