Read how the HTTP Protocol at least on the wiki
There is an http server that waits for connections on a port and processes requests.
Each request is characterized by a method (get, post, put, head, etc.), the address (and this is a separate factor, not correlated with the method), headers (where we have the client's wishes about the response format, all sorts of cookies, information about the client), a body (where we have the form data post requests, just downloadable files like avatars or json'and...).
Every such request gets to the server and gives him some kind of answer or even ignore closing or not closing the connection.
Write a post request is how to understand, write code to perform a post request (from client to server, of course, there is no other way).
If the server at the given address or for some other reason does not accept a post request, you will not be able client-side to get him to do it.
Even if you hit him with a stick.
The server you will meet with an error with some code. If server developers well done, the error code will be relevant to the situation, but generally there nt[ybxtcrb can be anything, even Devil 666 request success.
You have not shown here the source code of the server, did not show a code sample that you used is not even close to understand how the HTTP Protocol don't understand what you ask...
How do you expect to understand that you are responsible?