A requirement the spck.dev suite checks on UCP servers. The quoted text is the normative requirement; the citation links to the exact line of the pinned spec source it was taken from.
Initial Service and Capability Discovery, step 3: when the selected protocol version is a key in supported_versions, the Platform MUST verify that the fetched profile's ucp.version equals the supported_versions key it selected; on mismatch the Platform MUST NOT use that profile.
A deviation on a MUST fails the run and shows the requirement next to the actual response. Checks the suite cannot validate soundly are reported inconclusive or not-tested — never a silent pass. The full verdict semantics are on the grading rubric.
The hosted check covers the read-only surface; the CLI and GitHub Action run the full suite, including this check when your store declares the capability it belongs to.