Error 403 trying to get a list of messages (Gmail) and tasks (Google Tasks) with Apis

Question

I am working with VB.Net, I followed the instructions to get a list of messages (gmail api v1) and tasks (tasks api v1) from Google:

https://developers.google.com/gmail/api/v1/reference/users/messages/list https://developers.google.com/google-apps/tasks/v1/reference/tasks/list

But I get the error 403 (Insufficient permission) but my datagridview is filled with the following headers with empty cells:

Gmail:

HistoryId - Id - LabelIds - Payloads - Raw - SizeEstimate - Snippet - ThreadId - Etag

Tasks:

Etag - Items - Kind - NextPageToken

I checked my google developer console and all is well, the apis are activated.

I also use my xxxxxxxxx@developer.gserviceaccount.com (just in case).

Also follow the instructions of Drive and Calendar apis and these work fine but of Tasks and Gmail give me that problem.

I use credentials (client id and client secret) to enter.

I tried on Google api explorer and everything works fine.

How can I fix this error?

Here's my Tasks and Gmail codes:

        Imports Google.Apis.Auth.OAuth2
    Imports Google.Apis.Services
    Imports Google.Apis.Tasks.v1
    Imports Google.Apis.Tasks.v1.Data.Tasks
    Imports Google.Apis.Tasks.v1.Data
    Imports System.Collections.Generic
    Imports Google.Apis.Util.Store
    Imports System.Threading
    Imports System
    Public Class Form1
        Dim Secrets = New ClientSecrets()
        Dim scope = New List(Of String)
        Dim initializer = New BaseClientService.Initializer
        Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
            Secrets.ClientId = "MY CLIENT ID"
            Secrets.ClientSecret = "MY CLIENT SECRET"
        End Sub
        Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
            scope.Add(TasksService.Scope.Tasks)
            Try
                Dim credential = GoogleWebAuthorizationBroker.AuthorizeAsync(Secrets, scope, "My Gmail account or developer account &.GOOGLE.COM", CancellationToken.None).Result()
                initializer.HttpClientInitializer = credential
                initializer.ApplicationName = "APP NAME"
                Dim service = New TasksService(initializer)
                Me.DataGridView1.DataSource = retrieveAllTasks(service)
            Catch ex As Exception
                MsgBox(ex.ToString)
            End Try
        End Sub
        Public Shared Function retrieveAllTasks(service As TasksService) As List(Of Tasks)
            Dim result As New List(Of Tasks)()
            Dim request As TasksResource.ListRequest = service.Tasks.List("@default")
            Do
                Try
                    Dim Gtasks As Tasks = request.Execute()
                    result.AddRange(Gtasks.Items)
                    request.PageToken = Gtasks.NextPageToken
                Catch ex As Exception
                    MsgBox(ex.ToString)
                    request.PageToken = Nothing
                End Try
            Loop While Not [String].IsNullOrEmpty(request.PageToken)
            Return result
        End Function
    End Class


   Imports Google.Apis.Auth.OAuth2
Imports Google.Apis.Services
Imports Google.Apis.Tasks.v1
Imports Google.Apis.Tasks.v1.Data.Tasks
Imports Google.Apis.Tasks.v1.Data
Imports System.Collections.Generic
Imports Google.Apis.Util.Store
Imports System.Threading
Imports System
Imports Google.Apis.Gmail.v1
Imports Google.Apis.Gmail.v1.Data

Public Class Form1
    Dim Secrets = New ClientSecrets()
    Dim scope = New List(Of String)
    Dim initializer = New BaseClientService.Initializer
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Secrets.ClientId = "CLIENT ID"
        Secrets.ClientSecret = "CLIENT SECRET"
    End Sub

    Public Shared Function ListMessages(service As GmailService) As List(Of Message)
        Dim result As New List(Of Message)()
        Dim request As UsersResource.MessagesResource.ListRequest = service.Users.Messages.List("TARGET EMAIL")
        Do
            Try
                Dim response As ListMessagesResponse = request.Execute()
                result.AddRange(response.Messages)
                request.PageToken = response.NextPageToken
            Catch ex As Exception
                MsgBox(ex.ToString)
            End Try
        Loop While Not [String].IsNullOrEmpty(request.PageToken)
        Return result
    End Function
    Private Sub Button10_Click(sender As Object, e As EventArgs) Handles Button10.Click
        Try
            scope.Add(GmailService.Scope.MailGoogleCom)
            Dim credential = GoogleWebAuthorizationBroker.AuthorizeAsync(Secrets, scope, "XXXXXXXX@developer.gserviceaccount.google.com", CancellationToken.None).Result()
            initializer.HttpClientInitializer = credential
            initializer.ApplicationName = "APP NAME"
            Dim service = New GmailService(initializer)
            Me.DataGridView1.DataSource = ListMessages(service)
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub
End Class