> For the complete documentation index, see [llms.txt](https://docs.promotekit.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.promotekit.com/affiliate-links-setup/stripe-api.md). # Stripe API Go to Step 4 (PromoteKit Integration) in your PromoteKit setup tab to follow along with these instructions. We also have a video walkthrough for NextJS: {% embed url="" %} ## Add the PromoteKit Script to your Site The PromoteKit script will go on both your site's landing page (where you'll be sending referrals), and the page on your site / app where your customers checkout. It's ok if your marketing site and app site are on different subdomains - the cookie tracking works across all subdomains of a domain. A common setup would be embedding the script on your marketing site at yourdomain.com, and app domain at app.yourdomain.com. Copy this script and paste it within your site's \ or \ tags. ## Send the Referral ID to Stripe Once the script is embedded, the referral ID will be retrievable with JavaScript/TypeScript using `window.promotekit_referral`, or with PHP using `$_COOKIE['promotekit_referral']` You will need to pass this ID in the metadata field when [creating a Stripe checkout session](https://docs.stripe.com/api/checkout/sessions/create) or when [creating a Stripe subscription](https://docs.stripe.com/api/subscriptions/create). In the body of either of these API calls, include `promotekit_referral` within the metadata. {% code title="JavaScript Checkout Session Creation Example" %} ```javascript const session = await stripe.checkout.sessions.create({ success_url: 'https://example.com/success', cancel_url: 'https://example.com/cancel', metadata: { promotekit_referral: req.body.referral, }, line_items: [ {price: 'price_1OBQlV2eZvKYlo2CDL02DbMx', quantity: 1}, ], mode: 'subscription', }); ``` {% endcode %} ## Optional Step: Manually Tracking Signups If you want to attach referrals to affiliates manually when they signup to your service and before they have paid, you can use this function: ```typescript window.promotekit.refer(email, stripe_customer_id?) ``` Email is a required parameter, and stripe customer id is an optional parameter.