How to set up Square Checkout API with Node.js server?

Question

I am making a website for a company using Node.js and Express. I am making my own auth system with carts using Firebase and once they use the check-out button, my goal is to create a new payment link with Square's Checkout Link API.

I understand the structure of requests through the API as the documentation shows But I am lost on how to import the SDK so I can perform the API request.

This is the front-end code that send a POST request to my node.js server side index.js root file. I am using blank information just to test.

<script>
    function orderCart(){
      var products = []
      $.ajax({
        type: "POST",
        url: "/order",
        data: { data: products },
        success: function (response) {
          alert("Order placed, a receipt has been emailed to you.");
          console.log(response);
        },
        error: function (err) {
          alert("Error placing order:", err);
          console.error("Error placing order:", err);
        }
      });
    }

    $("#order").click(function(){orderCart()});
  </script>

The request gets received to my server-side code just fine, but when I try to make the request to Squares Checkout API, of course, it does not work because I have the code for the request but node.js has no idea what to do with it because I do not have the SDK Imported.

app.post('/order', async (req, res) => {
  const products = req.body.data;

  try {
    const response = await client.checkoutApi.createPaymentLink({
      idempotencyKey: '',
      description: '',
      order: {
        locationId: '-------',
        lineItems: [
          {
            name: 'Product Name',
            quantity: '1',
            itemType: 'ITEM',
            basePriceMoney: {
              amount: 2000,
              currency: 'USD'
            }
          },
          {
            name: 'Product 2',
            quantity: '2',
            itemType: 'ITEM',
            basePriceMoney: {
              amount: 5000,
              currency: 'USD'
            }
          }
        ],
        pricingOptions: {
          autoApplyTaxes: true
        }
      },
      checkoutOptions: {
        allowTipping: false,
        redirectUrl: '-------',
        merchantSupportEmail: '-------',
        askForShippingAddress: true,
        acceptedPaymentMethods: {
          applePay: true,
          googlePay: true,
          cashAppPay: false,
          afterpayClearpay: true
        },
        shippingFee: {
          name: 'Shipping Fee',
          charge: {
            amount: 0,
            currency: 'USD'
          }
        },
        enableCoupon: false,
        enableLoyalty: false
      }
    });
  
    res.status(200).send(response.result);
  } catch(error) {
    res.status(400).send(error);
  }
});

(Got rid of crucial info in the request for privacy)

I understand that no request will get sent because the documentation doesn't seem to specifically define how to import the required SDK. The SDK it says I need on the API reference page is /v2/online-checkout/payment-links. I got all of my information so far from the documentation page linked below. How would I go about importing the required SDK so it allows me to make valid requests to squares Checkout API?

https://developer.squareup.com/reference/square/checkout-api Please correct me if I am wrong but the documentation does not seem to be very useful.