Acrobat 2017 won't let me connect to SharePoint online site

In Acrobat 2017, I open a file and seek to save it to my SharePoint Online site.

I choose Save As > Add Account , and choose Add under the SharePoint Site icon.

I give it an account name and (working!) URL and press Continue.

When I click Continue, that dialog box simply blinks:  It disappears for 1/4 second, and then reappears just as pictured, still populated with my text, and ... nothing happens.

Help!