Making a Shopify API request from a Custom Pixel

[GregPotter]

I have created a custom pixel to send order data on "checkout_complete" to an application i've developed to upload orders to an erp software. I need to get the PO # of the shopify order that was placed. The checkout_complete hook only returns the order id. Can I make a request to the shopify API to get the PO # using the order id before sending a post request to my server?

Below is my code. Including a comment where I'd like to make the request.

analytics.subscribe('checkout_completed', (event) => {
  const checkout = event.data.checkout;

  const checkoutTotalPrice = checkout.totalPrice?.amount;

  const allDiscountCodes = checkout.discountApplications.map((discount) => {
    if (discount.type === 'DISCOUNT_CODE') {
      return discount.title;
    }
  });

  const firstItem = checkout.lineItems[0];
  const items = [];
  checkout.lineItems.map((item, index) => {
    const newItem = {
        sku: item.variant.sku,
        quantity: item.quantity,
        price: item.finalLinePrice?.amount,
    }
    items[index] = newItem;
  })

 /* items.forEach((item) => {
    console.log(item);
  })*/
  
  const billAdd = {
    firstName: checkout.billingAddress.firstName,
    lastName: checkout.billingAddress.lastName,
    address1: checkout.billingAddress.address1,
    address2: checkout.billingAddress.address2,
    city: checkout.billingAddress.city,
    country: checkout.billingAddress.country,
    province: checkout.billingAddress.province,
    provinceCode: checkout.billingAddress.provinceCode,
    zip: checkout.billingAddress.zip,
    phone: checkout.billingAddress.phone,
};
  const shipAdd = {
    firstName: checkout.shippingAddress.firstName,
    lastName: checkout.shippingAddress.lastName,
    address1: checkout.shippingAddress.address1,
    address2: checkout.shippingAddress.address2,
    city: checkout.shippingAddress.city,
    country: checkout.shippingAddress.country,
    province: checkout.shippingAddress.province,
    provinceCode: checkout.shippingAddress.provinceCode,
    zip: checkout.shippingAddress.zip,
    phone: checkout.shippingAddress.phone,
  };
  const email = checkout.email;
  const orderId = event.data.checkout.order?.id;

  /*make api request to shopify using orderId to get the order PO Number. */

  const payload = {
    event_name: event.name,
    event_data: {
      orderId,
      totalPrice: checkoutTotalPrice,
      discountCodesUsed: allDiscountCodes,
      billingAddress: billAdd,
      shippingAddress: shipAdd,
      email: email,
      items: items,
    },
  };
  
  console.log(payload);
  
  fetch('https://******/uploading-api', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(payload),
    keepalive: true,
  });
});