Going nuts trying to get API to work........

Going nuts trying to get API to work........

For the life of me I cannot get the API to POST any data using the format provided in the document.  I have no problem GET'ing records.

Here is a sample PHP script I made to be bare-bones simple.  Whenever I execute it, I get a "Invalid value passed for JSONString".

I know I'm missing something crazy simple.  Please let me know.  Sample code  below.

<?php

$zohoauthtoken = "XXXXXXXXXXXXXXXXXXXXXXXXXX";
$zohoorgid = "XXXXXXXXX";

$json_string = '{
        "contact_name": "test123",
}';

$post = array(
        'JSONString' => $json_string,
);


$headers = array(
        'Authorization' => "Zoho-authtoken $zohoauthtoken",
        'Content-Type' => "application/json;charset=UTF-8",
);

$ch = curl_init();
           curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
           curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
           curl_setopt($ch, CURLOPT_POST, TRUE);
           curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
           curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
           curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
           curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
           curl_setopt($ch, CURLOPT_URL, $url);
           $results = curl_exec($ch);
           curl_close($ch);
           error_log($results);
?>