Add extra section to upgrading in README

README.md

@@ -42,6 +42,12 @@ Before upgrading ensure that the **Admin API access scopes** match the [requirem
 
 After upgrading, ensure that all required webhooks have been created by clicking the “Create” button on the **Shopify** → **Webhooks** screen in your project’s control panel page in the CP. If the “Create” button is not visible, all required webhooks have been created.
 
+### From `3.x` to `4.x`
+
+In version `4.0.0` the plugin changed its Shopify API requirement to version `2023-10`. Any Shopify custom apps created before this version will need to update their webhook event version to `2023-10`.
+
+This can be done by visiting your Shopify store and going to **Settings** → **Apps and sales channels** → **Develop apps** clicking you app and then **Configuration** → **Webhook version**. 
+
 ### Create a Shopify App
 
 The plugin works with Shopify’s [Custom Apps](https://help.shopify.com/en/manual/apps/custom-apps) system.