Setting up Google as mail provider via OAUTH test connection fails

[nwd]

Hi folks, 

I have been trying to setup my G Suite email to be used as the Mail Provider via these instructions, which everything seems straight forward, but always hangs /locks up the console from several minutes when I click "test connection", and just sits there indefinitely, or if I click the x on the configure mail provider overlay, and reopen, can get it to provide an error. (see attached pics). 

WHMCS INSTRUCTIONS FOR SETTING UP google as the mail service provider

https://help.whmcs.com/m/system/l/1277316-setting-up-google-as-your-mail-service-provider

WHMCS is at the latest version of 8.1.3, I am using the GSUITE Legacy Free edition Gmail account (for past 10 years). 

Has anybody else run into this issue, or anybody using this feature yet?  And if successful, which G SUITE (workspace) edition are you licensed for? 

Thanks for any help.