Errors

Error shape

Failed requests return JSON with success: false and an error message:

{
  "success": false,
  "error": "Missing or invalid API key"
}

Status	Meaning	What to do
`400`	Bad request — invalid `action`, malformed `skus`, etc.	Fix the request body
`401`	Missing or invalid API key	Verify the `Authorization` header
`405`	Wrong HTTP method	Use `POST` only
`500`	Server error	Retry with exponential backoff
`502` / `503`	Upstream unavailable	Retry with backoff; contact Keystone if persistent

Use exponential backoff for 5xx responses.
400 and 401 errors are not retryable without changing the request.
For bulk syncs, paginate with limit / offset rather than sending very large skus arrays.