Handling errors

The API returns errors with an HTTP status code and a JSON body. The body contains a message.

Error reference

Errors returned by the AWS Events API

Status	Meaning	What to do
400	The API could not accept the request as sent. A field is missing, too long, or malformed. The API also returns this for a nextToken it did not issue.	Do not retry. Fix the request. The message says which field.
401	The operation needs a signed-in attendee, but you sent no valid token. The WWW-Authenticate header says where to sign in. An event that requires registration has no public catalog. For that event, ListSessions and GetSession return 401 to an anonymous caller.	Sign in, or refresh the token, then retry once. See Keeping the attendee signed in.
403	Two different causes, told apart by the body. With a JSON body, the caller is signed in but not registered for this event. That includes reading the catalog of an event that requires registration, so an unregistered caller gets 403 from ListSessions and GetSession too. With no body, the refusal came from the edge rather than the API, and requests from your address are being refused.	For a registration problem, do not retry. Register for the event first, because signing in again will not help. For an edge refusal, slow down, then retry.
404	The event, session, or personal time entry does not exist. For a removal, it is already gone.	Do not retry. For removals, treat it as already done.
409	The operation is not currently available. The request itself was valid.	Do not retry immediately. See When an operation is closed.
429	The caller has used up this operation's quota for the current minute.	Wait for Retry-After seconds, then retry. See Quotas and throttling.
500	The service hit an internal error. It could not process the request.	Retry a read with backoff. Before retrying a write, reconcile from GetSchedule. See Retrying a write safely. If it persists, report it using the Feedback link on this page.
503	The service is temporarily unavailable.	Retry a read with backoff. For a write, see Retrying a write safely.

When an operation is closed

An operation can close for a time while the rest of the API keeps working. A closed operation returns 409 to every caller. The request itself was not the problem. The same request will not succeed until the operation opens.

Reservations might be closed until reserved seating opens for an event. Browsing and favoriting keep working.

Retrying a write safely

The API has no idempotency key. Re-sending a create makes a new one. This matters for the two bulk operations and for CreatePersonalTime. If you never learned the outcome of one of those — a timeout, a dropped connection, a 500 or a 503 — do not simply re-send it. Read GetSchedule and compare it with what you intended. Send only what is still missing.

The single removals are different. Canceling a reservation or removing a favorite that is already gone returns 404, so a retry whose response you never saw is safe: treat 404 as already done.

A 429 and a 409 are also safe to retry later, because neither performed the write.