Add to cart button in Foodie theme shows "Unavailable" text

This is a know issue with Foodie theme, where the Foodie theme wrongly marks the product as "unavailable" when the product form contains the selling plan element. This means that this will happen with any subscription app you try, as the issue is coming from the theme.
The issue is coming from the following file: /assets/product.js
You can see in the screenshot where the issue is coming from. 

Unfortunately, we don't have control over your theme's code, so the best way to resolve this will b to contact your theme developers and ask them to adjust the theme OR use a different theme, which doesn't have this issue.