Youcanpay API php issue

Here is theSDK of youcanpay payment gateway https://github.com/NextmediaMa/youcan-payment-php-sdk

I have followed the documentation described in the above link. And the payment form is displaying fine but I need to generate a token to proceed with the payments. But in the token generating step php not able to find youcanpay class intances which is used as static method YouCanPay::setIsSandboxMode(true);. I simply want to be sure I didn't do anything wrong. May be there was an issue with my folder structure here it's screenshot https://i.imgur.com/uqdXgmr.png. Or I have to change php namcspace? use YouCan\Pay\YouCanPay;

Form display HTML

  <div id="error-container"></div>
    <div id="payment-card"></div>
    <button id="pay">Pay</button>

** php **
use YouCan\Pay\YouCanPay;

class ExamplePayment
{
    
    /**
     * Return a token to make payment for an order, this token is required to make payment with JS script.
     *
     * @return string
     */
    public function createToken()
    {

        // Enable sandbox mode, otherwise delete this line.
        YouCanPay::setIsSandboxMode(true);

        // Create a YouCan Pay instance, to retrieve your private and public keys login to your YouCan Pay account
        // and go to Settings and open API Keys.
          $youCanPay = YouCanPay::instance()->useKeys('pri_sandbox_56cfe571-f671-42a6-a231-d58ec', 'pub_sandbox_a62be70f-d585-4e88-9c5b-563f2');
        // $youCanPay = YouCanPay::instance()->useKeys('pri_sandbox_56cfe571-f671-42a6-a231-d58ec', 'pub_sandbox_a62be70f-d585-4e88-9c5b-563f2');

        // Data of the customer who wishes to make this purchase.
        // Please keep these keys.
    
        // Create the order you want to be paid
        $token = $youCanPay->token->create(
            // String orderId (required): Identifier of the order you want to be paid.
            "order-id",
            // Integer amount (required): The amount, Example: 25 USD is 2500.
            "2000",
            // String currency (required): Uppercase currency.
            "USD",
            // String customerIP (required): Customer Address IP.
            "175.107.236.174",
            // String successUrl (required): This URL is returned when the payment is successfully processed.
            "https://smmpanelauto.com/orders-status/success",
            // String errorUrl (required): This URL is returned when payment is invalid.
            "https://smmpanelauto.com/orders-status/error"
        );

        echo $token->getId();
    }
    
}

********** JS Code **********
   <script type="text/javascript">
        // Create a YouCan Pay instance.
        const ycPay = new YCPay('pub_sandbox_a62be70f-d585-4e88-9c5b-563f2', {
            formContainer: '#payment-card',
            locale: 'en',
            isSandbox: true,
            errorContainer: '#error-container',
            // token: 'token_x6gf0_....'
        });

        // render the form
        ycPay.renderCreditCardForm();
        
        // start the payment on button click
        var el = document.getElementById('pay');
        if(el){
            <?php   
                 $a = new ExamplePayment; 
                ?>
            el.addEventListener('click', function(){
                  // execute the payment
                  ycPay.pay("<?php $a->createToken(); ?>") //using token
                    .then(successCallback)
                    .catch(errorCallback);
                });
        }
        function successCallback(response) {
          console.log(rsponse);
        }
        
        function errorCallback(response) {
            console.log(rsponse);
        }
    </script>

When I use <?php $a->createToken(); ?> the form is not showing. otherwise. it's shows the following error There are invalid fields in your request, please verify your inputs and try again But all inputs are filled.