Callback URL not receiving JSON data - json

Question

I have a PHP page that receives JSON responses located at https://example.ac.ke/op/api/mypesa/index.php
I have success posting responses using Postman when I post to either
https://example.com/op/api/mypesa/
or
https://example.com/op/api/mypesa/index.php
but not when I post to
https://example.com/op/api/mypesa
I have tried redirecting and adding trailing / in htaccess in vain.
I need to make https://example.com/op/api/mypesa to be my callback URL. When I post the receiving page is called but it seems like the data is not redirected.
NEED HELP REDIRECTING BOTH PAGE AND POST DATA
Since I have success redirecting page but not the data
My .htaccess has the following content
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php [L,QSA]
</IfModule>
Posting using postman
database table receiving the json data from page
Posting using postman to the page
Content of my index file located in mypesa folder
<?php
require 'config.php';
header("Content-Type: application/json");
$response = '{
"ResultCode": 0,
"ResultDesc": "Confirmation Received Successfully"
}';
$mpesaResponse = file_get_contents('php://input');
$logFile = "M_PESAConfirmationResponse.txt";
$jsonMpesaResponse = json_decode($mpesaResponse, true);
$transaction = array(
':TransactionType' => $jsonMpesaResponse['TransactionType'],
':TransID' => $jsonMpesaResponse['TransID'],
':TransTime' => $jsonMpesaResponse['TransTime'],
':TransAmount' => $jsonMpesaResponse['TransAmount'],
':BusinessShortCode' => $jsonMpesaResponse['BusinessShortCode'],
':BillRefNumber' => $jsonMpesaResponse['BillRefNumber'],
':InvoiceNumber' => $jsonMpesaResponse['InvoiceNumber'],
':OrgAccountBalance' => $jsonMpesaResponse['OrgAccountBalance'],
':ThirdPartyTransID' => $jsonMpesaResponse['ThirdPartyTransID'],
':MSISDN' => $jsonMpesaResponse['MSISDN'],
':FirstName' => $jsonMpesaResponse['FirstName'],
':MiddleName' => $jsonMpesaResponse['MiddleName'],
':LastName' => $jsonMpesaResponse['LastName']
);
$log = fopen($logFile, "a");
fwrite($log, $mpesaResponse);
fclose($log);
echo $response;
insert_response($transaction);
?>