When I try to add a bitbucket account in Sourcetree:

I click "Connect Account", which opens a dialog for entering my credentials. I enter the correct credentials and Bitbucket opens successfully inside the dialog. However I cannot continue from here and the only thing I can do is to cancel the dialog which prevents me from adding the account.
I am on MacOS 10.13.5 and using v2.7.6. I have tried deleting the preferences and have also tried rolling back to previous version, i.e., v2.6.3 but no luck. :-(
Does anyone have any idea of how to fix this?