1.Why the new Shopify new preorder model is implemented
The App has been implemented Shopify’s new pre-order model in addition to the old preorder model of the app. We must do this based on request from Shopify. The new pre-order model is using Shopify Selling Plan API. When you convert to this new pre-order model, it will be applied for all new pre-orders the store has.
2.What about advantages and disadvantages of new pre-order model
Setting up pre-orders
***New features with the Selling Plan API
💰 Configure deposit amounts and due payments
Apps can configure a deposit due date at checkout and define when the remaining balance is owed. Shopify vaults the buyer’s payment method, allowing the app to capture the remaining balance automatically.
🚚 Set new types of fulfillment dates
Apps can describe when the product will be fulfilled, resulting in orders that have future or unknown fulfillment dates.
🏭 Delay inventory reservation until fulfillment occurs
Apps can configure selling plans to allow buyers to go through checkout without decrementing the inventory in a store. Inventory can be allocated when the initial order or fulfillment occurs.
👀 Track overdue payments
Merchants can track unpaid orders that go past their due date. Orders will receive a payment status change in the Order Index page.
***Requirements and restrictions with the Selling Plan API
You must have a reasonable basis for saying that a product can be shipped within a certain time.
If no date is clearly specified, you must have a reasonable belief that the product will ship within 30 days of purchase.
If you’re unable to ship within the promised time, you must provide a revised shipment date and explain the customer’s right to cancel or obtain a refund.
Customers need to use Shopify Payments or PayPal Express as a payment gateway.
Customers can’t purchase pre-orders by using the following accelerated checkouts: Shop Pay, Apple Pay, Google Pay, or Meta Pay.
Customers can’t use local payment methods such as Klarna, mollie iDEAL, and Sofort to purchase pre-orders.
Pre-orders aren’t supported through Shopify POS.
Pre-orders can’t be used on draft orders.
Buy X get Y discounts aren’t supported by pre-orders.
Each order can only have one deferred payment due date. If an order has multiple products that have different deferred payment due dates, all of the order’s deferred payments will be due on the soonest due date.
3.How to manage to convert to the New Preorder Model
Please go to app admin page → Preorder → Settings → New Pre-order model → click on Change to the new model → Save 
If you do encounter any difficulty while proceeding these steps, don’t show any hesitation to contact us promptly via the email address
We are always willing to help with all sincerity