Listen to events

These controllers tell you what is happening. The SDK behaves the same whether you implement them or not: use them to drive your own UI, or to answer the wallet sheet with new totals.

Controller	Fires when	Platforms
`onInstallmentSelected`	The shopper picks or changes an installment option in the card form.	Web (`card.onInstallmentSelected`), iOS, Android
`onShippingAddressChanged`	The shopper selects or changes the shipping address in a wallet payment sheet.	Web (`externalButtons.onShippingAddressChanged`), iOS, Android
`onChange`	The validity of the form the SDK rendered changes. The handler receives `{ form: { isValid } }` when the transaction starts and on every change. When you hide the SDK’s Pay button with `showPayButton: false`, use it to enable your own button before you call `transaction.submit()`.	Web

onInstallmentSelected and onShippingAddressChanged each have a page with what you receive, what you return and the signature per platform.

onStatus. The final outcome of the transaction.
Take over the SDK. The controllers that replace a default behavior.
Controllers overview. How controllers are wired per platform.

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