Public API errors

Every error response is an RFC 9457 Problem Details document (application/problem+json):

code is the stable machine string to branch on. type links to this page (https://developers.synthesia.io/docs/errors#<code>) — it's documentation, not an identifier, and its URL may change.
detail is human-readable and may change without notice; each code below shows example
messages ({braces} mark request-specific values).
requestId (also the Request-Id header) identifies the request in Synthesia's logs —
include it when contacting support.
New codes may appear over time; a rare unmapped 4xx surfaces as http_<status>, and an
unexpected 5xx keeps its status with code internal. Handle any response you don't
recognize by its HTTP status.

Status	`code`	`title`
400	`bad_request`	Bad request
400	`validation_error`	Invalid request
401	`api_key_expired`	API key expired
401	`unauthenticated`	Unauthenticated
402	`feature_not_in_plan`	Feature not in plan
402	`no_credit`	No credit
402	`payment_required`	Payment required
402	`quota_exceeded`	Quota exceeded
403	`forbidden`	Forbidden
403	`insufficient_scope`	Insufficient scope
404	`not_found`	Not found
404	`unknown_reference`	Unknown reference
405	`method_not_allowed`	Method not allowed
409	`conflict`	Conflict
413	`payload_too_large`	Payload too large
415	`unsupported_media_type`	Unsupported media type
429	`concurrency_limit`	Concurrency limit exceeded
429	`rate_limited`	Rate limit exceeded
500	`internal`	Internal error
503	`admission_unavailable`	Admission temporarily unavailable
503	`service_unavailable`	Service unavailable
504	`timeout`	Upstream timeout

`bad_request`

Bad request — status 400 — type

The request could not be parsed as sent — usually a body that is not JSON. Fix the request before retrying; an unchanged retry fails the same way.

Example detail messages:

The request body is missing or null. Send a JSON object.
The request body is not valid JSON. Send a JSON object.
The request body was not sent as JSON. Set the Content-Type header to application/json.

`validation_error`

Invalid request — status 400 — type

One or more request fields were rejected. Fix the fields detail lists and resend; an unchanged retry fails the same way.

For a rejected request body, detail lists each rejected field as path: message, joined with ; ; other validation denials use the standalone messages below.

Example detail messages:

Not a valid {concept} id.
One or more fields were rejected.
The supplied livekitToken cannot be used to join the room.

`api_key_expired`

API key expired — status 401 — type

The API key is genuine but past its expiry date. Not retryable with this key — create a new key and use it instead. The WWW-Authenticate: Bearer header carries error="invalid_token".

Example detail messages:

Your API key has expired. Create a new key and retry with it.

`unauthenticated`

Unauthenticated — status 401 — type

The request carried no usable API key. Send your key as Authorization: Bearer <key>. An unknown or revoked key is reported only as invalid; an expired key answers api_key_expired instead. The WWW-Authenticate: Bearer header carries realm alone when no key was sent, error="invalid_request" for an Authorization scheme other than Bearer, and error="invalid_token" for a rejected key.

Example detail messages:

Invalid API key.
Provide your API key in the Authorization header.
Unsupported Authorization scheme. Send your API key as 'Authorization: Bearer '.

`feature_not_in_plan`

Feature not in plan — status 402 — type

Your workspace's plan does not include a feature this endpoint requires; features names it. Not retryable — upgrade the plan or contact your account manager.

Example detail messages:

Your plan does not include interactive avatars — upgrade to use this API.
Your plan does not include the '{feature}' feature.

`no_credit`

No credit — status 402 — type

Your workspace has no credit remaining for the metered feature this request consumes. Not retryable until the balance is positive again — top up or upgrade your plan.

Example detail messages:

Your plan has no interactive avatar credits. Top up or upgrade to create interactive avatars.

`payment_required`

Payment required — status 402 — type

The request was declined for billing reasons, such as exhausted credits. Resolve the billing condition, then retry.

`quota_exceeded`

Quota exceeded — status 402 — type

A usage quota in your plan is used up. Not retryable until your quota is increased or replenished — upgrade your plan or contact your account manager.

Example detail messages:

Your session quota is exhausted.

`forbidden`

Forbidden — status 403 — type

Your API key is valid but not permitted to do this — the resource may belong to another workspace, or your account may lack the required permission. If you believe you should have access, check with your workspace admin.

`insufficient_scope`

Insufficient scope — status 403 — type

Your API key does not carry the scope this endpoint requires; detail names it, as does scope in the WWW-Authenticate: Bearer error="insufficient_scope" header. Use or create a key with that scope — retrying with the same key fails the same way.

Example detail messages:

Your API key does not have the '{scope}' scope this endpoint requires.

`not_found`

Not found — status 404 — type

Nothing exists at this URL. Check the path and any resource id in it.

`unknown_reference`

Unknown reference — status 404 — type

The request referenced a resource that does not exist or is not accessible to your workspace. Fix the referenced id and resend.

Example detail messages:

One or more of avatarIds does not exist or is not accessible.
The referenced avatar, outfit or person does not exist or is not accessible.

`method_not_allowed`

Method not allowed — status 405 — type

The URL exists, but not for this HTTP method. The Allow header lists the methods it supports.

`conflict`

Conflict — status 409 — type

The request conflicts with the resource's current state. Fetch the resource, reconcile, and resend.

`payload_too_large`

Payload too large — status 413 — type

The request body exceeds the size this endpoint accepts. Reduce the payload and resend.

`unsupported_media_type`

Unsupported media type — status 415 — type

The request's Content-Type is not one this endpoint accepts. Send the body as application/json unless the endpoint documents otherwise.

`concurrency_limit`

Concurrency limit exceeded — status 429 — type

Your plan's ceiling on concurrently running sessions is reached. Retryable — end an active session or wait for one to finish, honoring Retry-After when present.

Carries Retry-After when Enact sends a wait interval. When known, detail leads with the caller's plan numbers and keeps the guidance to end or wait for a session.

Example detail messages:

Too many sessions are running concurrently for your plan. End an active session or wait for one to end.

`rate_limited`

Rate limit exceeded — status 429 — type

Too many requests in the current window. Retryable — back off for the Retry-After interval, then resend the same request.

The facade's own denials carry RateLimit-Limit, RateLimit-Remaining, RateLimit-Reset-At and Retry-After headers; a domain's 429 carries at most Retry-After.

Example detail messages:

Too many requests. Retry after the interval in the Retry-After header.

`internal`

Internal error — status 500 — type

Something unexpected failed on Synthesia's side. Usually safe to retry; for a request that creates a resource, check whether the operation went through first. If it persists, contact support and quote the requestId.

Example detail messages:

An unexpected error occurred.

`admission_unavailable`

Admission temporarily unavailable — status 503 — type

A billing or rate decision this request needs could not be obtained, so it was denied rather than admitted unchecked. Transient — retry with backoff, honoring Retry-After when present.

Example detail messages:

Admission is temporarily unavailable. Retry shortly.

`service_unavailable`

Service unavailable — status 503 — type

A service this request needs is temporarily unavailable. Transient — retry with backoff, honoring Retry-After when present and any instruction in detail. If it persists, contact support and quote the requestId.

Example detail messages:

Authentication is temporarily unavailable. Retry shortly.
Plan features for this request could not be verified. Retry shortly.
Temporarily unable to create an interactive avatar. Retry the same request with regenerate off.
Temporarily unable to read credits. Retry shortly.
Temporarily unable to start a session. If you retry, reuse the same livekitUrl and livekitToken.
The session could not be started. Retry shortly.

`timeout`

Upstream timeout — status 504 — type

The request did not finish within its deadline. The underlying operation may still have gone through — follow the guidance in detail on how to retry or poll safely, otherwise retry with backoff.

Example detail messages:

Authentication is temporarily unavailable. Retry shortly.
Plan features for this request could not be verified. Retry shortly.
The request did not complete within its {deadline}s deadline.
The session did not start before the deadline. It may still start. If you retry, reuse the same livekitUrl and livekitToken.
Timed out reading credits. Retry shortly.
Timed out waiting for the avatar status. Generation may still be running; repeat the same request with regenerate off to poll.
Timed out waiting for the session to start. It may still start. If you retry, reuse the same livekitUrl and livekitToken.