How to do preorders

You can do pre-orders with the Waitlist feature by simply setting the inventory count for the product to 0 in Shopify:

This will automatically trigger the waitlist message for anyone who comments for it:
Then when you get the product in stock. Update the inventory appropriately in Shopify. This automatically triggers the "back-in-stock" messages for anyone on the waitlist:

You can wait up to 1-year to get your inventory. And the app will appropriately message everyone when you update the inventory.

Shopify does not allow for pre-authorizations. But you can charge the customer's credit card for the purchase if you select this option in Shopify:

Selecting this option avoids the waitlist, and lets the shopper check out to purchase. And then you would fulfill the order when inventory becomes available