Resolve problems with getting Gmail accounts to work with POSitive.
First, configure your account to use POP:
Login to your Gmail account, then click the gear icon, then choose Settings > Forwarding and POP/IMAP. Enable POP, then click Configuration instructions link.
https://support.google.com/mail/answer/12103?hl=en
If you still can't get it to work, go through the Troubleshoot Problems section on the same page.
https://support.google.com/mail/answer/7104828
Next, if you're NOT using 2-Step Verification then be sure that you enable Less Secure Apps.
https://support.google.com/accounts/answer/6010255
If you ARE using 2-Step Verification, then you'll need to generate a Google account App Password
https://support.google.com/accounts/answer/185833
