require 'vendor/autoload.php';

<?php
use Yellow\Bitcoin\Invoice;
$api_key = "Your API public key";
$api_secret = "Your API Private key";
$yellow = new Invoice($api_key,$api_secret);
/// this will return an array with invoice data
$paylaod = array(
    "base_price" => 10,
    "base_ccy"   => "USD",
    "callback"   => "http://yourstore.local/checkout/status/"
);
$invoice  = $yellow->createInvoice($payload);
var_dump($invoice);
/// this will return an array with invoice status data
$status = $yellow->checkInvoiceStatus($invoice["id"]);
var_dump($status);

 <?php
 use Yellow\Bitcoin\Invoice;
 $api_key = "Your API public key";
 $api_secret = "Your API Private key";
 $yellow = new Invoice($api_key,$api_secret);
 $isValidIPN = $yellow->verifyIPN($url, $signature, $key, $nonce, $body); //bool
 var_dump($isValidIPN);