An HTTP POST request sends data from the web client to the web server. Unlike an HTTP GET request, a POST request includes a body containing data (although this body could be zero-length).
The POST body format can vary, and it should be identified by a Content-Type header. Many modern, web-based APIs expect a POST body to be JSON encoded.
Consider the following HTTP POST request:
POST /orders HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0)
Content-Type: application/json
Content-Length: 56
Connection: close
{"symbol":"VOO","qty":"10","side":"buy","type":"market"}
In the preceding example, you can see that the HTTP POST request is similar to an HTTP GET request. Notable differences are as follows: the request starts with POST instead of GET; a Content-Type header field is included; a Content-Length header field is present; and an HTTP message body is included. In that example, the HTTP message body is in JSON format, as specified by the Content-Type header.