My Salesforce @RestResource class is having three methods to handle PUT, POST, and GET. But when i am trying to invoke POST from external system, GET method is getting invoked.
When i try to invoke PUT and GET, they are getting invoked correctly. The issue is with POST response only. No idea why GET is getting invoked when i try to POST. Below is my class, and i am using POSTMAN to monitor PUT, POST, and GET responses.

This issue is exclusive when we try to attempt to POST using "http". You will not see this issue if you try to POST using "https".
We need to find a solution to this, as my current project needs an end point to POST using only "http".

Any information regarding this is greatly appreciated!

@RestResource(urlMapping='/myapi/IVAPIInterface/*')
global without sharing class REST_IVAPI {

    @HttpPost
    global static string doPost() {
        RestRequest req = RestContext.request; 
        System.debug('req is---------------------- ' +req); 
        return 'happy';
    }

    @HttpPut
    global static string doPut() {
        RestRequest req = RestContext.request; 
        System.debug('req is---------------------- ' +req); 
        return 'Put';
    }

    @HttpGet
    global static string doGet() {
        RestRequest req = RestContext.request; 
        System.debug('req is---------------------- ' +req); 
        return 'Get';
    }
}