Server errors are grouped by numbers that always start with the digit 5, the ones that commonly occur are:
500 Internal Server Error
It is the most common error and occurs when the web server is unable to process a request made by the website, the most frequent causes of which are associated with the permissions of files and folders on the website, PHP language version , or incorrect or inappropriate instructions contained in the file. htaccess of the site;
502 Bad Gateway
This is an error related to a network problem, more specifically in the communication between two points in the network, one of which is the server on which the website is located and the other, for example, a server from your ISP;
If you are setting up your business, you do need to think about the type of network that you need. There are two main options to consider here. These are LAN vs WAN cable networks.
503 Service Unavailable
It also occurs when the server is unable to respond to a request, but it is usually associated with overhead. Although it is an error condition that in fact represents an error on the server and not on the website or network, the cause may not be related to the server itself, as in cases where a website is exceeding a hosting account limit, for example DDoS attack , for example;
504 Gateway Timeout
It is a less common error to occur, but it is also likely to be found. Contrary to what many people imagine, it is unusual or rare that you make a direct access to a server that hosts a website, but that uses another server that acts as a gateway (port) or proxy that directs data traffic to the destination . When the time that the gateway or proxy has to receive the result of the request is exceeded, the error occurs;
505 HTTP Version not supported
Currently it should be very rare to find this type of error, but it is possible, particularly when accessing very old and outdated equipment. This is because the HTTP error in question is due to old and insecure versions of the protocol, which in turn presupposes old browsers.