This is a PHP based implementation of PayPay's SDK. For the demonstration purpose we have used a simple Flask server with polling library to create QR code link and to check the order status of a QR code

composer install

export API_KEY="REPLACE_WITH_YOUR_API_KEY"
export API_SECRET="REPLACE_WITH_YOUR_SECRET_KEY" 
export MERCHID="REPLACE_WITH_YOUR_MERCHANT_ID"

cd src
php -S localhost:5000

You should now have the API server running on http://localhost:5000