I'm doing a fresh install of sourcetree 3.1.3 and when I click on the BitBucket link on the Registration page it takes me to the BitBucket oauth url with a redirect_uri=http://localhost:34106/ parameter.
That page loads with
So I am unable to proceed with the installation.
Sorry to hear about this problem with logging into a Bitbucket account from Sourcetree. However this is not just you that is having this problem. There is currently an outage in regards to Bitbucket Cloud's OAuth tokens are not working correctly. This is the cause of the inability to login here and in turn showing that 'Invalid redirect_uri' error message.
Atlassian has just updated our StatusPage about this incident that you can use to track this problem in https://bitbucket.status.atlassian.com/incidents/l50d1j43zdj9
I would recommend subscribing or watching that incident for update. Once this incident is resolved I would expect that you should then be able to use Sourcetree without this error.
Sorry again for the inconvenience here.