This is a PHP class i made for myself to use in a project I’m working on. It is a work in progress. My goal is to make the API as simple to use as possible while keeping it customizable.

PayPalAP::setAuth('my_api_username', 'my_api_password', 'my_api_signature'); // I'm not passing in an environment, which will default it to sandbox mode.
$options = array(
    'cancelUrl' => 'https://my_cancel_url',
    'returnUrl' => 'https://my_return_url',
    'currencyCode' => 'USD',
    'receiverEmailArray' => array('receiver_of_funds'),
    'receiverAmountArray' => array('15'),
    'ipnNotificationUrl' => 'https://my_ipn_listener_url'
);
$response = PayPalAPI::doPayment($options); // If the options is valid, the user is redirected to PayPal to do the payment (and there will be nothing to read in the $response variable). If not, the errors will be returned from the function.

Because of PayPal’s silly naming scheme of the Adaptive Payments IPN values, you cannot read the IPN content from the $_POST global.

Instead, you will have to collect the raw data and create an array. This array can then be passed to our class function.

$raw_post_data = file_get_contents('php:https://input');
$raw_post_array = explode('&', $raw_post_data);

$data_array = array();
foreach($raw_post_array as $keyval) {
    $data = explode("=", $keyval);
    if(count($data) == 2){
        $data_array[$data[0]] = urldecode($data[1]);
    }
}

Now we have a simple array with keys and values. Time to pass it to the IPN handler in our class.

if(PayPalAP::handleIpn($data_array)) {
	// Payment is verified. Check if this payment has been processed before etc. before taking any actions.
} else {
	// Payment is not verified. Log this incident and discard.
}