Charging a deposit upon scheduling is easy with Shopify product variants. You can learn more about variants here on the Shopify Help Center.
Here is a visual guide to accompany that help article as it would relate to our app.
Here is how you get what you see above setup.
From your Shopify admin navigate to "Products" and select the product that you want to add a deposit variant to. Next, scroll to the "Options" section and check the box "This product has options, like size or color"
Once checked you'll be shown variant form fields. Follow the example here to create:
Your new variants will now populate:
That's it! Don't forget to use the "Save" button in Shopify.