Null response from postman in graphql

I am getting a null response in data when executing a query on postman but the query works fine in graphiQL. I am using anonymous auth and am passing bearer access token in header.
Query:

query getContacts  {
    contact_collection {
        _id
        contacts{
            name
            email
            phone
        }
        user_id
    }
}

Response:

{
    "data": {
        "contact_collection": null
    }
}

Hi Ashutosh – Often when we see folks reporting this it is related to how their Rules are set-up. Can you confirm that the user that you have authenticated with has the ability to read this data?

If you DM me a link to your application I can take a closer look.