Gmail API throws 401: error login required only for sending emails

问题

I'm trying to set up the gmail api to send emails automatically using google's sample code. When trying to send an email, I receive a 401 error.

I've set up quickstart and given it access to my gmail for all purposes. I can access my account through the API for other purposes, such as retrieving labels, but not sending emails. I've tried deleting and remaking my token several times, and I have set SCOPES to include sending emails and that shows up in my google account.

def create_message(sender, to, subject, message_text):

    message = MIMEText(message_text)
    message['to'] = to
    message['from'] = sender
    message['subject'] = subject
    return {'raw': base64.urlsafe_b64encode(message.as_bytes())}

with open('token.pickle', 'wb') as token:
    creds=pickle.load(token)

service = build('gmail', 'v1', credentials=creds)
results = service.users().labels().list(userId='me').execute()
labels = results.get('labels', [])
print(labels)

#this script works up to here

message = service.users().messages().send(userId='me', body=create_message('myemail@gmail.com', 'testemail@gmail.com', 'Test', '')).execute()
print('Message Id: %s' % message['id'])
print(message)

As expected, the labels print correctly, but I receive the following error for trying to send the message:

HttpError: <HttpError 400 when requesting
https‍://www.googleapis.com/gmail/v1/users/me/messages/send?alt=json returned "'raw' RFC822 payload message string or uploading message via /upload/* URL required">

which leads to:

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "required",
    "message": "Login Required",
    "locationType": "header",
    "location": "Authorization"
   }
  ],
  "code": 401,
  "message": "Login Required"
 }
}

来源：https://stackoverflow.com/questions/56225578/gmail-api-throws-401-error-login-required-only-for-sending-emails