The 502 Bad Gateway Error is an indication that something has gone wrong within the server of your application, as opposed to the client side request.
How to Fix a 502 Error
Perform a hard-refresh in your browser. On Macs, this is done by pressing Cmd + Shift + R.
This problem is due to poor IP communication between back-end computers, possibly including the Web server at the site you are trying to visit. Before analysing this problem, you should clear your browser cache completely.
If you get this problem for only some of the Web sites you try to visit then it is likely to be a problem at those sites i.e. one of their pieces of equipment is failing/overloaded. Contact the people at those sites.
If you are surfing the Web and see this problem for all Web sites you try to visit, then either 1) your ISP has a major equipment failure/overload or 2) there is something wrong with your internal Internet connection e.g. your firewall is not functioning correctly. In the first case, only your ISP can help you. In the second case, you need to fix whatever it is that is preventing you reaching the Internet.
In some cases, this error caused by low computer hard disk space, you can go check the free space of your computer hard disk. If there is really not enough free space left, clean your computer hard disk well.
Start your browser in Safe Mode. Running a browser in Safe Mode means to run it with default settings and without add-ons or extensions, including toolbars.
If your web application is configured to listen on a socket, ensure that the socket exists in the correct location and that it has the proper permissions
Finally, restart your computer/networking equipment. Some temporary issues with your computer and how it's connecting to your network could be causing 502 errors, especially if you're seeing the error on more than one website. In these cases, a restart would help.