# Web Checkout Links

Learn how to use campaigns and placements to present web paywalls using Superwall's web checkout links.

Once you've [created a Stripe app](/docs/web-checkout/web-checkout-creating-an-app), [configured Stripe with Superwall](/docs/web-checkout/web-checkout-configuring-stripe-keys-and-settings) via the [Superwall Stripe app](https://marketplace.stripe.com/apps/superwall) and have [created Stripe products](/docs/web-checkout/web-checkout-adding-a-stripe-product) — you're ready to configure a campaign to show a web paywall.

> **Note**

Before you proceed, recall that web checkout has all of the advantages of the Superwall platform. If you are unfamiliar with how to create campaigns or what a placement is — we recommend you read through the [introduction](/docs/using-the-dashboard) documentation and [campaigns doc](/docs/dashboard/dashboard-campaigns/campaigns) first.



Understanding placements in web checkout [#understanding-placements-in-web-checkout]

There are two primary differences between web checkout and the typical Superwall campaign flow:

1. **Placements become unique URLs** which, in turn, show your paywall. These are called *web checkout links*.
2. **User variables** are not available in audience filtering.

Other than that, everything operates as a normal Superwall campaign would. For example:

<img src="__img0" />

Here, the placement `black-friday-promo` presents a paywall. If the app's URL in [settings](/docs/web-checkout/web-checkout-configuring-stripe-keys-and-settings) is `caffeinepal`, then the URL for this placement would be `https://caffeinepal.superwall.app/black-friday-promo`. Visiting that web checkout link presents a paywall:

<img src="__img1" />

Conceptually, you can think of these web checkout links performing a similar function as registering a placement does in our mobile SDK:

```swift
Superwall.shared.register(placement:"black-friday-promo") { _ in }
```

This means that you now can use web checkout with all of the same powerful features that Superwall offers, such as A/B testing, paywall targeting and more. Again, these work just like any other campaign would in Superwall. The interface is the same, so now you create placements, start creating audience filters and more:

<img src="__img2" />

Also, remember to create responsive paywalls. Users can view your checkout page on a laptop, phone and other varying sized viewports. For some quick tips, check out this blog post over adapting paywalls to look great on [iPad](https://superwall.com/blog/how-to-create-adaptable-paywalls-for-iphone-and-ipad-using-superwall).

A note on the `$home` placement [#a-note-on-the-home-placement]

Every campaign has a `$home` placement out of the box. This placement acts a "default" link, and isn't required to be part of the URL as other placements are. For example:

```plaintext
// This works 
https://caffeinepal.superwall.app/$home

// And this also works, even though `$home` isn't in the URL
https://caffeinepal.superwall.app/
```

This is useful so that even if a user visits your web checkout link, and there isn't a placement in the URL — they'll still see a paywall.

How query string parameters work [#how-query-string-parameters-work]

You can attach query string parameters to any web checkout link by appending them to the URL:

```html
https://caffeinepal.superwall.app/black-friday-promo?name=jordan
```

This will pass the `name` parameter to the placement, and you can use it in your audience filters. For example, you could create a filter that only shows the paywall if the `name` parameter is equal to `jordan`:

<img src="__img3" />

Or, you could access them in your paywall using the same flow as you would for [placement parameters](/docs/using-placement-parameters):

1. In the paywall editor, add a variable.
2. Make it a `parameter` type. Match the `name` to the query string parameter key (here, that would be `name`).
3. Set the value type, then click **Create**.
4. Now, you can use that variable in your paywall:

This makes it easy to show in your paywall:

<img src="__img4" />

Then, if the URL is visited, the audience filter matches from above — and we can see the value on the paywall, too:

<img src="__img5" />

Of course, this is a simplistic example — but this is useful for personalization, seasonal events, influencer campaigns and more. Any query string parameter you pass can be used in the paywall, and in audience filters.

Localized checkout prices [#localized-checkout-prices]

Web checkout links support [Stripe Adaptive Pricing](/docs/web-checkout/web-checkout-adaptive-pricing). When Adaptive Pricing is enabled in Stripe, customers can see localized currency in the Stripe checkout flow based on their location.

This does not change how you build campaigns or placements in Superwall. Create the web checkout link as usual, then let Stripe localize the checkout price when the customer starts payment.

Automatically populating user emails in checkout flows [#automatically-populating-user-emails-in-checkout-flows]

> **Tip**

This section is Web2App only (starting from a web link). For App2Web (starting from an iOS paywall), see [App2Web](/docs/web-checkout/web-checkout-direct-stripe-checkout#prefill-email).



There is a special query string parameter you can use to automatically populate the user's email in the checkout flow. This is useful for pre-filling the email field in the checkout form, so that users don't have to enter it manually. Simply add `email` and set the value to the user's email address:

```html
https://caffeinepal.superwall.app/black-friday-promo?email=myemail@yahoo.com
```

When the Stripe checkout flow launches, the email is now filled out automatically:

<img src="__img6" />

Automatically populating appUserId in checkout flows [#automatically-populating-appuserid-in-checkout-flows]

There is a set of special query string parameters which will set the appUserId for the subscription. This overrides the default behavior where Superwall will automatically assign an anonymous identifier. You may pass `uid`, `user`, or `app_user_id` to override the default.

```html
https://caffeinepal.superwall.app/black-friday-promo?app_user_id=my-custom-id
```

This identifier will show up in Stripe metadata & webhooks. The app\_user\_id will be put into the `client_reference_id` field on a Stripe Checkout Session and will be included on the subscription metadata under `_sw_app_user_id`