/**
 * The client secret to hand `initCheckoutElementsSdk()` / `initCheckoutFormSdk()`, from the
 * `fetchClientSecret` or else the `clientSecret` prop. Stripe.js checks a secret Promise in a
 * chain of its own that nothing handles, so a rejected one, or one resolving to anything but a
 * non-empty string, ended up uncaught even with `loadActions()` handled (#697). The failure
 * goes to `fail` instead, worded as in VueStripeEmbeddedCheckout, and Stripe gets a Promise that
 * never settles.
 */
export declare function checkedSecret(props: {
    clientSecret?: string | Promise<string> | undefined;
    fetchClientSecret?: (() => Promise<string>) | undefined;
}, fail: (message: string) => void): string | Promise<string>;