The 502 bad gateway can occur when your computer's server tries to connect to the QuickBooks server and it fails. Often times if you refresh your screen by holding CTRL+R on Windows / CMMD + R on Mac, you should be able to reload QuickBooks.
If you're still receiving the 502 bad gateway, could you let us know what browser are you using to log in to QuickBooks?
Thanks for getting back to us with additional information, murphycivil.
I've checked here and haven't found any open investigation about the error message when using the Desktop application. I recommend performing some basic troubleshooting to get back on track with using QuickBooks.
Let's start with clearing cache through these steps:
Check out this screenshot for a visual reference on the steps:
If the error continues, please proceed with uninstalling and reinstalling the application. For the detailed instructions, I recommend clicking the article below (scroll down to How do I uninstall the app?):
You'll also see some information I found helpful, such as the updated system requirements on the link above.
Whenever you need further help fixing the error, don't think twice to post. The Community will keep an eye on your response.