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Referralful credits an affiliate using whichever signal it can find at the time of the sale. Pick the method that matches how your site and billing are set up.

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Quick guide

MethodNeeds the snippet?Works across separate domains?
Referral link (cookie)YesSame registrable domain only (apex + subdomains)
Pass the referral idCapture onlyYes — any domains
Coupon codeNoYes — any domains
Customer emailYes (to track the lead)Same registrable domain only
A visitor lands on yourbrand.com/?via=token. The snippet stores the referral in a cookie on your registrable domain (.yourbrand.com), so it is shared across the apex and every subdomain automatically — yourbrand.com, www.yourbrand.com, and app.yourbrand.com all see it. Each page that starts checkout needs the snippet loaded so window.AffID.referral is available.
The cookie is shared across subdomains of one registrable domain. If your marketing site and app are on completely different domains (e.g. brand-marketing.com and brandapp.io), the cookie cannot bridge them — use method 2 or 3 below.

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2. Pass the referral id (separate domains)

Capture window.AffID.referral on the landing page, carry it with the user (store it on their account, or pass it through your signup URL), and send it as referral_id when they pay: 
curl https://api.referralful.com/v1/conversions \
  -u rfl_live_your_secret: \
  -H "Content-Type: application/json" \
  -d '{ "referral_id": "ref_abc123", "amount_cents": 4900, "external_id": "invoice_12345" }'
This works no matter how many domains are involved, because you carry the id yourself.

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3. Coupon codes (cookieless)

Give each affiliate a promo code. When a customer uses it, the sale is attributed by the code — no link, no cookie, no snippet required. This is the most robust option for fully separate domains or sites you can’t add JavaScript to. Assign a code to an affiliate: 
curl https://api.referralful.com/v1/affiliate_coupons \
  -u rfl_live_your_secret: \
  -H "Content-Type: application/json" \
  -d '{ "affiliate_id": "aff_123", "token": "ALEX20" }'
Then:
  • Stripe — when the customer applies the coupon (or promotion code) at Checkout, Referralful reads it from the webhook and credits the affiliate automatically.
  • Any other billing — pass the code as coupon when reporting the sale: 
    curl https://api.referralful.com/v1/conversions \
  -u rfl_live_your_secret: \
  -d '{ "coupon": "ALEX20", "amount_cents": 4900, "external_id": "invoice_12345" }'

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4. Customer email

If the visitor was tracked as a lead (snippet on the marketing site) and later pays, Referralful can match the sale by the customer’s email. Pass email to /v1/conversions, or it resolves automatically for Stripe. This needs the lead to have been tracked first, so it shares the same-domain limitation as the cookie.