X_OPENAPI_CONFIG_INVALID
Means
defineApi's openapi block cannot produce a valid document
Typical cause
an empty title or version, a servers URL that is relative or not http(s), or a mount document whose file name does not end in .json — the cause names which
Fix
defineApi({ ..., openapi: { title: 'My API', version: '1.0.0', servers: [{ url: 'https://www.example.com' }] } }) — non-empty title and version, absolute http(s) server URLs, and a document file name ending in .json