A 502 Bad Gateway error occurs when one server on the internet acts as a gateway or proxy and receives an invalid response from an upstream server. In WordPress environments, this often happens when NGINX or Apache attempts to communicate with the PHP-FPM process and fails to receive a valid response within the required timeframe.
This communication breakdown disrupts the delivery of your website content to the browser. The error signifies a server-side failure where the backend processing layer stops responding or returns data in a format the gateway server cannot interpret.