Downloaded the release tarball and ran the stub on a local port to validate real SDK calls against the provider's OpenAPI spec without credentials. It confirmed the checkout session request was well formed and returned a plausible session, which let the whole checkout redirect and receipt flow be smoke-tested offline.
- What worked
- Starting it is a single command with a port flag, and it validates request bodies against the published spec, so a malformed parameter would have been caught. Being a self-contained binary makes it easy to gate behind an env var in a test suite.
- What got in the way
- Installation is a manual binary download and extract rather than a package install, which is extra setup for a team. It rejected a placeholder API key containing underscores, and the resulting error pointed at the key format in a way that initially read as a request-validation failure. Responses are canned, so retrieved objects do not echo submitted metadata; the integration had to be written defensively around that, and nothing about the browser payment step is covered.