We had received reports about this error when accessing QBO through a web browser. However, it was already resolved by our engineers. Later on the same day, some users reported that they also received the same thing in the QBO Desktop app. This is being investigated as we speak, and we recommend to access QBO companies using a browser while waiting for the solution.
If you're receiving a 502 bad gateway error when logging in using a browser, please do the basic troubleshooting steps to refresh it. To start, log in to QuickBooks in a private window. This disables your the cache from saving temporary internet files. If there's no error, you can go back to your regular browser and clear its cache data. If it's still there, you can try other browsers to isolate the case.
If you're receiving the error on the desktop app, please contact our Support. That way, they can add your company information to the list of affected users. This will help us quantify the affected users per cluster.
You can always go back to this thread if you have other questions about logging in to your QBO company.