Shopify native store credit only functions if your store uses Shopify's New Customer Accounts and is only available for logged-in users. It is completely incompatible with Legacy Customer Accounts and Guest Checkout.
Before opting into this feature, ensure you can answer yes to the following questions:
Do we currently use New Customer Accounts?
Do we actively enforce or strongly encourage users to log in?
What happens if a guest or unauthenticated user requests store credit?
If a guest checkout customer initiates a return, Shopify cannot apply native store credit because there is no authenticated customer profile to bind the financial ledger to.
How do I check if New Customer Accounts is enabled in Shopify?
Navigate to your Shopify Admin > Settings > Customer accounts. Ensure that New Customer Accounts is selected as your default experience, and verify that the Store Credit toggle within that menu is switched on.