# Checkout (iOS SDK)

The checkout flow wraps the complete payment experience, allowing users to select a payment method, then creates and pays the invoice.

![Tilia Hosted Checkout](/assets/ios-checkout-final.98af8bf6729684924566682b61937005c34dec479de4a5f1c693aae0552178dc.9c1bb791.png)

### Prerequisites

- Authorized User Password Token (A User Password Token is a string that enables Tilia Wallet to verify that a request belongs to an authorized session)
- Authorized Invoice ID (The ID for the Authorized invoice you created - see more info below)


All methods and flows in the Tilia SDK require you to have a server setup that communicates with Tilia’s APIs (your server will have a private api key which needs to remain secure and should never be exposed to client-side applications). Your client application should communicate with your own api (ensuring user authentication) to retrieve data required by the Tilia SDK.

#### Server-Side Code Example to create an Authorized Invoice and retrieve required information for the SDK

- Requires your server to retrieve a client credentials access token. See more [here](/authentication).
- Requires an account id for a user that has been registered with Tilia. See more [here](/guides/register-user).
- Requires a payload outlining the details of your Authorized Invoice. See more .



```json
curl --location --request POST 'https://invoicing.staging.tilia-inc.com/v2/authorize/invoice' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer CLIENT_CREDENTIALS_ACCESS_TOKEN' \
--data-raw '{
   "account_id": "USER_ACCOUNT_ID",
   "is_escrow": false,
   "invoice_mechanism": "api",
   "reference_type": "My test order",
   "reference_id": "123456789",
   "line_items": [
       {
         "description": "Line item 1",
         "product_sku": "ABC123",
         "transaction_type": "user_to_integrator",
         "currency": "USD",
         "amount": 1,
         "recipients": []
       },
       {
         "description": "Line item 2",
         "product_sku": "DEF456",
         "transaction_type": "user_to_integrator",
         "currency": "USD",
         "amount": 2,
         "recipients": []
       },
       {
         "description": "Line item 3",
         "product_sku": "GHI789",
         "transaction_type": "user_to_integrator",
         "currency": "USD",
         "amount": 3,
         "recipients": []
       }
   ]
}'
```

#### Example Response Payload


```json
{
   "status": "Success",
   "message": [],
   "codes": [],
   "payload": {
       "authorized_invoice_id": "AUTHORIZED_INVOICE_ID",
       "password_token": "AUTHORIZED_USER_PASSWORD_TOKEN"
   }
}
```

Your api should return the `authorized_invoice_id` and `password_token` to your client application to use in the Tilia SDK.

### Swift Code Example


```swift
let yourViewControllerForPresenting = UIViewController()
TLManager.shared.setToken("AUTHORIZED_USER_PASSWORD_TOKEN")
TLManager.shared.presentCheckoutViewController(on: yourViewControllerForPresenting,
                                               withInvoiceId: "AUTHORIZED_INVOICE_ID",
                                               animated: true,
                                               onUpdate: { onUpdate in print(onUpdate.description) },
                                               onComplete: { onComplete in print(onComplete.description) },
                                               onError: { onError in print(onError.description) })
```

### Demo App Example

You can see an example of the Checkout flow in our demo application.  See more [here](/sdks/ios-demo-app)