How can I redirect users back to my website after completing a payment on Shopify using the Shopify Buy button integrated on my Webflow CMS collection, and is it possible to pass parameters to Shopify to track which user (Memberstack) has made a payment?

To redirect users back to your website after completing a payment on Shopify using the Shopify Buy button integrated on your Webflow CMS collection, you can follow these steps:

1. Create a "Thank You" page on Webflow: Start by creating a separate page on your Webflow site that you want users to be redirected to after completing the payment. This page can be designed to thank the user for their purchase or provide any other relevant information.

2. Configure the Shopify Buy button: In your Webflow CMS collection, locate the Shopify Buy button element that you've integrated for payment. Click on the element to access its settings.

3. Set the redirect URL: Within the Shopify Buy button settings, look for an option to set the "redirect URL" or "return URL" and enter the URL of your "Thank You" page that you created in Webflow.

4. Save and publish: Save and publish your changes to ensure that the updated settings take effect.

By setting the redirect URL within the Shopify Buy button element, once a user completes the payment on Shopify, they will automatically be redirected back to your designated "Thank You" page on your Webflow site.

Regarding passing parameters to Shopify to track which user (Memberstack) has made a payment, you can accomplish this through the use of the Shopify's JavaScript API.

1. Capture user information: In your checkout flow, capture the necessary information about the user, such as their unique identifier or any other relevant details. You can leverage the Memberstack API to retrieve this information.

2. Prepare the Shopify Buy button: In your Webflow CMS collection, make sure your Shopify Buy button element has a unique identifier, such as an ID or class name. This will allow you to target the element in JavaScript.

3. Implement JavaScript code: On your Webflow site, add custom JavaScript code to listen for the completion event of the Shopify Buy button. When the event is triggered, you can use the Shopify JavaScript API (e.g., `Shopify.push()` or `ShopifyBuy`) to pass the captured user information as parameters to Shopify.

Here's an example of how the JavaScript code might look:

```javascript
document.addEventListener('DOMContentLoaded', function() {
var shopifyBuyButton = document.querySelector('.your-shopify-buy-button-class'); // Replace with the actual class name of your Shopify Buy button element

shopifyBuyButton.addEventListener('click', function() {
// Retrieve user information from Memberstack API
var user = MemberStack.currentUser; // Replace with the code to retrieve user information from Memberstack

// Pass user information as parameters to ShopifyShopify.push({  name: 'user\_id',  value: user.id});

});
});
```

In this example, the code listens for the click event on the Shopify Buy button and retrieves the user information from Memberstack. Then, it passes the user's ID as a parameter named `user_id` to Shopify using the `Shopify.push()` method.

By implementing this approach, you can track which user (Memberstack) has made a payment on Shopify by passing the necessary parameters. Remember to replace the placeholder values with your actual class names, IDs, and API calls in the code snippet.