Refresh the Page:

Sometimes, a temporary glitch may cause the 502 error. Refresh the page to see if the problem persists.

Clear Browser Cache:

Cached data in your browser can sometimes lead to errors. Clear your browser cache and try accessing QuickBooks Online again.

Use a Different Browser:

Try accessing QuickBooks Online using a different web browser to see if the issue is browser-specific.

Check Intuit's Status Page:

Intuit maintains a status page where you can check if there are any ongoing issues with their servers. Visit the Intuit status page to see if there are any reported problems: Intuit Status

Wait and Try Again:

If the issue is on Intuit's server side, waiting for some time and trying again later might resolve the problem.

Regards,
Peter