Could not get permission from Google

Hi Support,

I tried this plugin and follow the instruction here:
https://wphowto.net/gmail-smtp-plugin-for-wordpress-1341

But I couldn’t get permission from google after I clicked Allow. I tried many times and it give me an error like this:
http://prntscr.com/qk8tay

What’s wrong? Not a good day today?

Please help me on this~~
Thanks so much~
Stone