How to Fix a 502 Bad Gateway Error on Your WordPress Site

When it comes to WordPress, there are a lot of different errors that can be downright frustrating and confusing. A few that come to mind are the white screen of death or the frightening error establishing a database connection. But an even more popular one is the 502 bad gateway error. Why? Because this regularly happens around the entire web, not only to WordPress sites, but even popular services such as Gmail, Twitter, and Cloudflare. But of course, we really only care about how it impacts your WordPress site. Read more below about what causes this error and some solutions on how to quickly resolve it. What is a 502 Bad Gateway Error?
Every time you visit a website your browser sends a request to a web server. The web server receives and processes the request, and then sends back the requested resources along with an HTTP header and HTTP status code. Typically an HTTP status code isn’t seen unless something goes wrong. It’s basically the servers way of notifying you that something has gone wrong, along with the code on how to diagnose it.
There are many different types of 500 status error codes (500, 502, 503 504, etc) which all have slightly different meanings. These
Source: https://managewp.org/articles/16024/how-to-fix-a-502-bad-gateway-error-on-your-wordpress-site

source https://williechiu40.wordpress.com/2017/09/01/how-to-fix-a-502-bad-gateway-error-on-your-wordpress-site/