Error while resolving signing key for kid due to /undefined/v1/keys jwks error

I am following the example here: https://developer.okta.com/blog/2018/06/06/node-api-oauth-client-credentials

When I attempt to access a protected resource I get an error: “Error while resolving signing key for kid…” with an inner exception from JwksClient: “Invalid URI “undefined/v1/keys””

It looks like the keys endpoint is incorrect, but I am not sure where this is coming from. I am simply using the default auth server: ISSUER=https://dev-XXXXXX.oktapreview.com/oauth2/default

Any help would be greatly appreciated!