I just installed a new Sourcetree version on an old computer. When setup for the new version of Sourcetree starts it states that I need to be registrated on Bitbucket. I can choose to use Bitbucket Server or Bitbucket. Clicking on Bitbucket it opens the browser to https://bitbucket.org/site/oauth2/authorize where I am already logged in but just a message appears:
This integration is misconfigured. Contact the vendor for assistance.
Sorry to hear about this problem with logging into a Bitbucket account from Sourcetree. There is currently an outage in regards to Bitbucket Cloud via OAuth logins 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 get Sourcetree to login to Bitbucket again via this OAuth method.
Sorry again for the inconvenience here.