Yes, this can be done. You have most of the outline and the idea already. I think a rough outline of steps would be like this:

1. Zapier triggers on every shopify purchase
2. Use the customer’s email address to lookup a row in Google Sheets
3. If found, the current customer was referred and the original customer’s (the referrer’s) email address is returned in the ‘found’ results.
4. You will have to add a custom property to the original customer in Klaviyo, which will trigger a Flow in Klaviyo to deliver the gift card. → Or you can trigger the email in Klaviyo via API/webhook

The challenge here, and it’s just because I’m not intimately familiar with Shopify anymore, is attaching the actual gift card or a link to the gift card in the email.

Hi ​@Amy Aylett 

Try using this Zap action: Shopify - Create Gift Card

Hey ​@Amy Aylett 👋

How did you get on with the suggestions from DavidLGS and Troy here? Were you able to get the referral flow set up?

Let us know how it’s going, want to make sure you’re all set!