Graph client access

Question

im trying to get access to graph account in windows service app. this is my code.

IConfidentialClientApplication clientApplication = ConfidentialClientApplicationBuilder
.Create(ObjectId)
.WithClientId(clientId)
.WithTenantId(TenantID)
.WithClientName(UserName)
.WithClientSecret(SecretValue)
.Build();

    var authProvider = new ClientCredentialProvider(clientApplication);
    GraphServiceClient graphClient = new GraphServiceClient(authProvider);

    IUserRequestBuilder client = graphClient.Users[clientId];


    var messages = await client.MailFolders["Inbox"].Messages
    .Request()
    .Expand("attachments")
    .GetAsync();

    foreach (var mssg in messages)
    {//do my things}

in the "await client.MailFolders["Inbox"].Messages" line i get Status Code: NotFound Microsoft.Graph.ServiceException: Code: ResourceNotFound Message: User not found

thanks for any answer