Unable to get user's email ID in user_friends API of Facebook

I'm fetching the list of user's friends who all are using the application with Login with Facebook feature. In GraphAPI for "user_freinds" request, I'm requesting for id, email & name of the users. However the API is not returning the email of users. Only name and ID of users are being returned. Please check the code below.

func getFacebookFriends() {
    if AccessToken.current != nil {
        let fbUserID = AccessToken.current?.userId ?? ""
        let friendsPath = "/\(fbUserID)/friends"
        let params = ["fields": "id, name, email"]
        let fbFriendsRequest = GraphRequest(graphPath: friendsPath, parameters: params, httpMethod: .GET)
        fbFriendsRequest.start { (_, result) in
            switch result {
            case .success(let response):
                print(response.dictionaryValue as Any)
                let responseDict = response.dictionaryValue!
                let data = responseDict["data"] as! [[String:Any]]
                if data.count != 0 {
                    // Sync the list with API
                } else {
                    // Show error 
                }
            case .failed(let error):
                // Show error
            }
        }
    }
}

Is there anything I'm missing here?

Also note that I'm using test users of Facebook, created by Developer portal of Facebook. Friends are added and authorised via Developer portal only.