How to pass required arguments to a custom content type with services?
1) Firstly you will create your custom resource for POST request.
Add Below Code to your module file.

function Your_Module_Name_services_resources() {
     $resources = array();
     //$_SERVER['REQUEST_METHOD'] = 'POST';
     //Include the necessary inc files.
    module_load_include('inc', 'Your_Module_Name', 'includes/Your_Module_Name.services');

   //Service Apis for contents.
    $resources += Your_Module_Name_resource();
    return $resources;
}


2) Create Your_Module_Name.services.inc file and write below code for your custom callback as given below.

function Your_Module_Name_resource() {
  $api = array(
'applicant_validate' =&gt; array( // Resource Name
 'operations' =&gt; array(
    'create' =&gt; array(
    'help' =&gt; 'Validate Applicant',
    'file' =&gt; array(
        'type' =&gt; 'inc',
        'module' =&gt; 'your_module_name',
        'name' =&gt; 'includes/your_module_name.services',
    ),
    'callback' =&gt; 'your_callback_function_name',
    'access callback' =&gt; 'user_access',
    'access arguments' =&gt; array('access content'),
    'access arguments append' =&gt; FALSE,
    'args' =&gt; array(
        array(
        'name' =&gt; 'body',
        'type' =&gt; 'string',
        'description' =&gt; 'Function to perform',
        'source' =&gt; 'data',
        'optional' =&gt; FALSE,
        'default' =&gt; '0',
        ),
    ),
    ),
    ),
  ));
   return $api;
 }


// variable name $body as you mentioned above in args part with name      parameter

function your_callback_function_name($body) 
{
  // It's called when you will hit to your web service url from your from submission.

}    

&lt;h2&gt;Validate Web Service&lt;/h2&gt;
 &lt;form id="frm" method="post" action="http://example.com/api/endpoint/applicant_validate"&gt;
 &lt;input type="text" placeholder="Application Id" name="appno" id="appno"/&gt;  
 &lt;input type="text" placeholder="Email Id" name="emailid" id="emailid"/&gt;
&lt;input type="text" placeholder="Mobile Number" name="mobno" id="mobno"/&gt;
&lt;input type="text" name="userpwd" placeholder="Password" id="userpwd"/&gt;
&lt;input  type="submit" value="submit"/&gt;&lt;br/&gt;
&lt;/form&gt;