Stripe webhook payload shape comes from the endpoint's pinned API version, not the SDK version

Each webhook endpoint stores its own api_version, set when the endpoint was created and readable from the endpoint object. Stripe renders event.data.object using that version regardless of which version your server library sends on outbound requests. A codebase whose client is pinned to a recent version can therefore receive events shaped for a version from years earlier, which in TypeScript appears as a type that compiles cleanly while the field is undefined at runtime. The event's own api_version field records which rendering you actually received.

Confirm by comparing event.api_version against the client's configured version. When upgrading, create a second endpoint at the new version and run both in parallel rather than mutating the existing one, because the change also affects retries already in flight.