Heavy server traffic or overloading can lead to the 502 Bad Gateway error. This may happen during peak hours when many users are accessing QuickBooks simultaneously.
A 502 Bad Gateway Error occurs when you try to visit a web page, but one web server gets an invalid response from another. Normally, the problem is on the website itself, and there’s nothing you can do. Other times, this error occurs because of a problem with your computer or networking equipment.