Error: Firebase ID token has no "kid" claim

Question

Firebase documentation states that custom claims can be accessed like so:

admin
  .auth()
  .verifyIdToken(idToken)
  .then((claims) => {
    if (claims.admin === true) {
      // Allow access to requested admin resource.
    }
  });

I have implemented Firebase auth following this sample project and tutorial. Specifically, the token is being decoded inside Next.JS' getServerSideProps here.

It's also worth mentioning that I'm running this project in development mode with Firebase Emulators.

So, on calling:

verifyIdToken(token)

I get this error message:

Error: Firebase ID token has no "kid" claim. See https://firebase.google.com/docs/auth/admin/verify-id-tokens for details on how to retrieve an ID token.

Any idea where I'm failing?

---------- UPDATE ----------

The decoded token has this info:

{
   "header":{
      "alg":"none",
      "typ":"JWT"
   },
   "payload":{
      "email":"user@test.test",
      "email_verified":false,
      "auth_time":1626004181,
      "user_id":"MY_USER_ID",
      "firebase":{
         "identities":{
            "email":[
               "user@test.test"
            ]
         },
         "sign_in_provider":"password"
      },
      "iat":1626004181,
      "exp":1626007781,
      "aud":"MY_FIREBASE_PROJECT_ID",
      "iss":"https://securetoken.google.com/MY_FIREBASE_PROJECT_ID",
      "sub":"SOME_KEY"
   }
}