HTTP (and HTTPS) are the protocols used by every browser to talk to web applications. A key part of the protocol is the HTTP method. Traditionally, web applications used a very limited set of HTTP methods such as GET (retrieve a web page) and POST (submit a web form).
Modern web applications, such as WooCommerce POS, use a REST/HTTP approach with following HTTP Methods:
In some rare cases a web host may choose to block some of these HTTP methods. If your web host blocks modern RESTful HTTP methods you will need to enable legacy server support.