Unable to fetch data from $_POST variable in PHP to Android Studio - php

Question

I want to fetch the content of $_POST variable from a PHP hosted file into Android app. I have tried using Jsoup and Volley libraries to do this but they were not producing the expected result. Later, found out that echo ("anyString"); is being fetched to android but echo($_POST["orderId"]); is not being fetched even though it gets printed in web page. Is there any way of solving this issue?
This is the PHP code:
<?php
$secretkey = "7457645673urgjnjkf784jyj66545y";
$orderId = $_POST["orderId"];
$orderAmount = $_POST["orderAmount"];
$referenceId = $_POST["referenceId"];
$txStatus = $_POST["txStatus"];
$paymentMode = $_POST["paymentMode"];
$txMsg = $_POST["txMsg"];
$txTime = $_POST["txTime"];
$signature = $_POST["signature"];
$data = $orderId.$orderAmount.$referenceId.$txStatus.$paymentMode.$txMsg.$txTime;
$hash_hmac = hash_hmac('sha256', $data, $secretkey, true) ;
$computedSignature = base64_encode($hash_hmac);
if ($signature == $computedSignature) {
echo json_encode($_POST);
}
?>
The java code in Android:
URL link = new URL("https://sample.php");
HttpURLConnection conn;
conn = (HttpURLConnection) link.openConnection();
conn.setReadTimeout(READ_TIMEOUT);
conn.setConnectTimeout(CONNECTION_TIMEOUT);
conn.setRequestMethod("POST");
conn.setDoOutput(true);
int response_code = conn.getResponseCode();
// Check if successful connection made
if (response_code == HttpURLConnection.HTTP_OK) {
// Read data sent from server
InputStream input = conn.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
StringBuilder result = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
result.append(line);
}
Log.d("result", result.toString());
}
}catch (Exception e){
Log.d("result", e.toString());
}