Hello @aldo, I think you are might be experiencing a CORS issue because you are using an authentication provider https://docs.mongodb.com/realm/authentication/#authentication-providers in the header, instead of using a Bearer access token.

Check out this documentation where you can find how to implement the authentication mechanism using an access_token instead https://docs.mongodb.com/realm/web/graphql-apollo-react/#set-up-user-authentication

I hope you found my explanation useful. Please do not hesitate to contact me if you need any further clarification