Use PayPal Express

Overview

Use the getPayPalExpressCheckoutRedirectURL method to retrieve the RedirectURL by sending an Order object with PAYPAL_EXPRESS payment method.

Parameters

Response

Retrieve PayPal redirect URL

<?

require ('PATH_TO_AUTH');

$Order = new stdClass();
$Order->Language = 'fr';
//$Order->LocalTime = date('Y-m-d G:i:s');
$Order->CustomerReference = 'APITEST';//uniqid('TESTCUSTOMER:');
$Product = new stdClass();
$Product->Code = 'my_subscription_1';
$Product->Quantity = 1;
$Order->Items[] = $Product;
$Order->Currency = 'EUR';
$Payment = new stdClass();
$Payment->Type = 'PAYPAL_EXPRESS';
$Payment->Currency = 'EUR';
$Payment->CustomerIP = '91.220.121.21';

$PayPalExpress = new stdClass();
$PayPalExpress->Email='customer@email.com';
$PayPalExpress->ReturnURL = 'http://' . $_SERVER['HTTP_HOST'] . '/api/place_order_api_soap_paypal_express_response.php';
$PayPalExpress->CancelURL = 'http://' . $_SERVER['HTTP_HOST'] . '/api/place_order_api_soap_paypal_express_response.php' . '?cancel=true';
$Payment->PaymentMethod = $PayPalExpress;    
$Order->PaymentDetails = $Payment;
// Call the method for retrieving Express Checkout redirect URL
$redirectUrl = $client->getPayPalExpressCheckoutRedirectURL($sessionID,$Order);
header('Location:' . $redirectUrl);

Place order with PayPal Express 

<?php
declare(strict_types=1);

class Configuration
{
    public const MERCHANT_CODE = '';
    public const MERCHANT_KEY = '';
    public const URL = 'http://api.2checkout.com/soap/6.0';
    public const ACTION = 'placeOrder';
    public const ADDITIONAL_OPTIONS = null;
    //array or JSON
    public const PAYLOAD = <<<JSON
{
  "Country": "us",
  "Currency": "USD",
  "CustomerIP": "91.220.121.21",
  "ExternalReference": "SOAP_API_AVANGTE",
  "Language": "en",
  "Source": "testAPI.com",
  "BillingDetails": {
    "Address1": "Test Address",
    "City": "LA",
    "State": "California",
    "CountryCode": "US",
    "Email": "testcustomer@2Checkout.com",
    "FirstName": "Customer",
    "LastName": "2Checkout",
    "Zip": "12345"
  },
  "Items": [
    {
      "Code": "A90B3D8FDE",
      "Quantity": 1
    }
  ],
  "PaymentDetails": {
    "Currency": "USD",
    "CustomerIP": "91.220.121.21",
    "PaymentMethod": {
      "RecurringEnabled": false,
      "ReturnURL": "http://secure.avangate.local/test/index.php",
      "CancelURL": "http://secure.avangate.local/test/create_order.php"
    },
    "Type": "PAYPAL"
  }
}
JSON;
}

class Client
{
    public function call(
        string $url = Configuration::URL,
        $payload = Configuration::PAYLOAD,
        string $action = Configuration::ACTION
    ): ?object {
        if (is_array($payload)) {
            $payload = json_encode($payload);
        }
        if (!empty($payload)) {
            // SoapClient works with objects(StdClass)
            $payload = json_decode($payload);
        }
        $soapClient = $this->getClient($url);
        $sessionId = $this->getSession($soapClient);
        $args = array_filter([$sessionId, $payload]);

        return $soapClient->$action(...$args);
    }

    public function getClient(string $url): SoapClient
    {
        return new SoapClient(
            $url.'?wsdl',
            [
                'location' => $url,
                'cache_wsdl' => WSDL_CACHE_NONE,
            ]
        );
    }

    public function getSession(SoapClient $client)
    {
        $date = gmdate('Y-m-d H:i:s');
        $merchantCode = Configuration::MERCHANT_CODE;
        $key = Configuration::MERCHANT_KEY;
        $string = strlen($merchantCode).$merchantCode.strlen($date).$date;
        $hash = hash_hmac('md5', $string, $key);
        $client->__setCookie('XDEBUG_SESSION', 'PHPSTORM');

        return $client->login($merchantCode, $date, $hash);
    }
}

try {
    $client = new Client();
    var_dump($client->call());
} catch (Exception $ex) {
    var_dump($ex);
}

Workflow 

1. Authentication via login API method.
2. Retrieve PayPal redirect URL. When you retrieve the PayPal redirect URL, apart from the token you will also receive 2 parameters that are encoded: billingDetails and deliveryDetails. These have to be base64_decoded and the information should be used in the placeOrder API call (email, billing address etc.). 
3. Place the order with PayPal Express using the token sent by PayPal.