Go to Settings and find Referral cookie duration (under the section where you set approval and referral options).
Enter a value between 1 and 3650 days. This is how long the referral (e.g. ?ref=CODE) stays valid for attribution; after that, a new click is required to attribute a sale to that affiliate.
Save. The new duration applies to future referral clicks; existing cookies keep their current expiry until they’re updated on the next visit.
Prevent self-referrals is in the same area if you want to block the store owner (or same customer) from earning referral credit.
The Settings guide gives more context on referral and onboarding defaults.