Variant product not adding to basket with price ?!

Hi everyone. I was hoping someone can point me in the correct direction. I’m trying to add a variant to a product when adding to cart, which gives it a unique price. This calls my server and then calls Shopify API. Now where I’m at works great, but the issue I’m having is it takes a good 15–30 seconds for this product to appear in the basket. The weird thing is, if I send the customer to check out instantly, the product is there with price and an image. Is there any way I can make the basket any faster ? Here’s my code :

The HTML ( product ID as been replaced)

<form id="customPriceForm">
  <input type="hidden" id="productId" name="productId" value="1231231231231"> 
  <input type="number" id="customPrice" name="customPrice" placeholder="Enter Your Price" step="0.01" required>
  <button type="submit">Create Variant and Add to Cart</button>
</form>

<script src="{{ 'TESTjava.js' | asset_url }}"></script>

Client side JavaScript

document.getElementById('customPriceForm').addEventListener('submit', async function(event) {
    event.preventDefault();
    try {
        const productId = document.getElementById('productId').value;
        const customPrice = document.getElementById('customPrice').value;

        // Show loading indicator to the user here
        console.log('Processing...');

        const createVariantResponse = await fetch('https://**MYSERVER**/create-dynamic-variant', {
            method: 'POST',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({ productId, customPrice })
        });

        if (!createVariantResponse.ok) {
            throw new Error('Network response was not ok when creating variant');
        }

        const data = await createVariantResponse.json();
        if (!data.success || !data.variantId) {
            throw new Error('Failed to create variant.');
        }

        console.log('Variant created:', data);

        const cartResponse = await fetch('/cart/add.js', {
            method: 'POST',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({
                id: data.variantId,
                quantity: 1
            })
        });

        if (!cartResponse.ok) {
            throw new Error('Network response was not ok when adding to cart');
        }

        const cartData = await cartResponse.json();
        console.log('Variant added to cart:', cartData);
        window.location.href = '/checkout'; // Redirect to cart when the price is correct

    } catch (error) {
        console.error('Error:', error);
        // Handle errors (e.g., show message to user)
        // Hide loading indicator here if shown
    }
});

Server side :

app.post('/create-dynamic-variant', async (req, res) => {
    const { productId, customPrice } = req.body;

    // Validate input to ensure required parameters are present
    if (!productId || !customPrice) {
        return res.status(400).json({ 
            success: false, 
            message: 'Missing required parameters: productId and customPrice.'
        });
    }

    try {
        // It's efficient to keep try-catch blocks as small as possible
        const product = await shopify.product.get(productId);
        const variantTitle = "CG#" + Math.random().toString(36).substring(7); // Simplified variantTitle generation

        const newVariant = await createVariant(productId, variantTitle, customPrice);

        // If newVariant is not created, throw an error
        if (!newVariant) {
            throw new Error('Variant creation failed');
        }

        console.log(`Variant created successfully: ID ${newVariant.id}, Title "${newVariant.title}", Price ${newVariant.price}`);
        res.status(200).json({ success: true, variantId: newVariant.id, message: 'Variant created successfully.' });
    } catch (error) {
        console.error('Error creating dynamic variant:', error.message || 'Unknown error');
        res.status(500).json({
            success: false,
            message: 'Error creating dynamic variant.',
            errorDetail: error.message || 'Unknown error'
        });
    }
});

// Refactored variant creation into a separate function for clarity and reusability
async function createVariant(productId, variantTitle, customPrice) {
    return shopify.productVariant.create(productId, {
        title: variantTitle,
        price: customPrice,
        inventory_management: null, // Indicates not to track inventory for this variant
        inventory_policy: 'deny',
        option1: variantTitle, // Setting option1 to the dynamically generated variant title
    });
}

Any help or method to make it quicker would be much appreciated :).

Thank you !

Can anyone help with this ?