Error 131056 · HTTP 400
Pair rate limit hit
The rate limit that applies to one conversation, not your account.
Cause. Too many messages between this business and this specific contact in a short period. Scoped to the pair, not the account.
Fix. Back off for that contact. Returned as 4xx, so a naive client-error rule fails it permanently.
Pair-scoped, not account-scoped
This is a cap on messages between your business and one specific contact in a short period. The rest of your sending is unaffected, which makes it different from 130429 and 131048 despite all three arriving as HTTP 400.
Treating it as an account-wide throttle means pausing a send that did not need pausing. Treating it as permanent means discarding a conversation that would have resumed within the hour.
Why it is usually your own doing
Pair limits are typically reached by automation talking to one person too quickly: a sequence firing several steps in close succession, or a retry loop that treats the refusal as transient and immediately tries again.
The correct response is a backoff for that contact only, and a look at whatever produced several messages to one person in a short window.
The whole table, free
Every code we document, with the handling decision each one implies, as an open dataset. The flags are generated by running the same classifier our production send path uses, so it cannot describe behaviour the software does not have. CC-BY, CORS open.