Cors issue and its relationship with http options verb (preflight check)

First lets understand cors:

A resource makes a cross-origin HTTP request when it requests a resource from a different domain than the one which the first resource itself serves. For example, an HTML page served from http://domain-a.com makes an <img> src request for http://domain-b.com/image.jpg. Many pages on the web today load resources like CSS stylesheets, images and scripts from separate domains.

Http verb OPTION:

The OPTIONS verb is a preflight request sent by some browsers to check the validity of cross origin requests. It pretty much checks with the server that the Origin(requester) is allowed to make the request for a specified resource. Also, depending on which headers are sent back by the server it lets the browser know which headers, methods, and resources the origin is allowed to request form the server.

The browser sends the OPTIONS request then if the server answers back with the correct headers (CORS headers) allowing the origin to make the request, you should see your POST request go through afterwards.

for more info go

There are multiple way we can fix the cors issue, a detail documentation is available here