Callbacks

Fired when session data has been fetched and the checkout is ready for input.

const sdk = FastSpring.init({
    checkoutUrl: '...',
    onSessionLoaded: (data) => {
        document.querySelector('#loading-spinner').hidden = true;
    },
});

Fired after a successful payment and order completion.

const sdk = FastSpring.init({
    checkoutUrl: '...',
    onOrderCompleted: (data) => {
        window.location.href = `/confirmation?order=${data.id}`;
    },
});

Fired when a payment attempt is rejected or encounters an error. The checkout stays open — the customer can correct their details and try again.

const sdk = FastSpring.init({
    checkoutUrl: '...',
    onPaymentFailed: (error) => {
        document.querySelector('#error-message').textContent =
            'Payment failed. Please check your card details and try again.';
    },
});

💡

onPaymentFailed fires on payment rejection — not on session load failure. For session load errors, use the onError callback on sdk.checkout().

Fired when the session loads successfully and the checkout is ready for input. No arguments.

sdk.checkout('<SESSION_ID>', {
    onSuccess: () => {
        console.log('Checkout is ready.');
    },
});

Fired when the session fails to load.

sdk.checkout('<SESSION_ID>', {
    onError: (error) => {
        console.error('Session load failed:', error);
    },
});

Common causes:

• Session ID is invalid or malformed
• Session has already been used
• Session has expired

⚠️

Create a fresh session immediately before each sdk.checkout() call. Sessions are single-use and expire — pre-creating or reusing them is the most common cause of this error.