Validating Genesys Cloud JWT in React implicit grant

Trying to validate the access token locally in a React app using the implicit grant flow. The payload looks valid, but verifying it against the JWKS endpoint at https://login.mypurecloud.com/.well-known/jwks.json fails the signature check.

jwt.verify(token, publicKey, { algorithms: ['RS256'] })

Getting an invalid signature error. Am I fetching the wrong key ID?