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err:frontline:capacity:openapi_validation_busy
The request matches an OpenAPI validation policy, and the gateway is too busy validating other requests to check this one. You get 503 Service Unavailable.
Example response
Browsers get the same error as an HTML page.

If you’re calling an API hosted on Unkey

Retry after a short delay, with backoff.

If you own this API

If you see this often under normal traffic, contact support.
Last modified on October 30, 2026