Crowd Control uses the product and shipping settings of your store to give backers a $0 checkout during survey completion. Items exceeding their pledge credit, i.e. add-ons and upsells, are billed through your preferred Shopify payments during checkout.
The following articles will help you get started with navigating this key part of survey setup.
Rewards & perks - Items offered to backers for their pledge.
Add-ons & upsells - Items that backers can purchase during their survey process.
Bundled rewards - Pledge levels containing multiple items.