How to use payment gateway POST webhook data in PHP

Question

I am making a payment gateway of instamojo, i am done payment making option i dont know how to handle Webhook after payment:

A sample POST webhook data will look something like this:

{
 'amount': '2500.00',
 'buyer': '[email protected]',
 'buyer_name': 'John Doe',
 'buyer_phone': '9999999999',
 'currency': 'INR',
 'fees': '125.00',
 'longurl': 'https://www.instamojo.com/@dalan/264a89803cec4401862f01e28f720eca',
 'mac': '1ddf3b78f84d071324c0bf1d3f095898267d60ee',
 'payment_id': 'MOJO5a06005J21512197',
 'payment_request_id': '264a89803cec4401862f01e28f720eca',
 'purpose': 'FIFA 16',
 'shorturl': 'https://imjo.in/NNNXn',
 'status': 'Credit'
}

Note that the webhook request’s content type is application/x-www-form-urlencoded.

Please give me any example.

I have tried to receive as below but not working

$data = $_POST;
$data = json_decode($data, true);

But its not working, so please help me.