title: Insufficient Permission [403] error while modifying the Message Label using gmail API in c#
body: <p>I am trying to read the gmail mail message, using gmail api, and after reading the mail, I am removing the message label, so that I don't need to process it again. I am able to read the mail successfully, but when I am trying to modify the message Label<br>
  (<code>service.Users.Messages.Modify(mods, userId, messageId).Execute();</code>)  </p>
  
  <p>then I am getting the error message:</p>
  
  <blockquote>
    <p>An error occurred: Google.Apis.Requests.RequestError<br>
        Insufficient Permission [403]<br>
        Errors [<br>
                Message[Insufficient Permission] Location[ - ]    Reason[insufficientPermis<br>
        sions] Domain[global]><br>
        ].  </p>
  </blockquote>
  
  <p>I am not able to figure out, what may have gone wrong?
  Thanks in advance.</p>