I just installed Mailbox Lite, then paid $4.99 for the upgrade.
Excuse me if I'm misunderstanding the situation but it looks like this thread started nearly a year ago, was added to as recently as a week ago, and all I see is a message from Halfbit that it's being worked on.
I'd like my $4.99 back.
I have tried to resolve this myself too. I ended up reinstalling Chrome several times and continue to get no fix for the matter. I have to admit that I'm surprised that Google would continue to allow people to purchase an upgrade knowing this matter remains unresolved. I use SalesforceIQ and can't get it to work with this app. Why have the app? Simply using the Google email from browser is enough when this feature has no value.