The specified Checkout Session could not be found

You may see an error like this when using Stripe Checkout:

The specified Checkout Session could not be found. This error is usually caused by using the wrong API key. Please make sure the API keys used to initialize Stripe.js and create the Checkout Session are test mode keys from the same account.

If you are using doing this on behalf of a Stripe Connected account then be sure to use the connected account ID when initializing the Stripe JS library like so:

var stripe = Stripe('{{PLATFORM_PUBLISHABLE_KEY}}', {
stripeAccount: '{{CONNECTED_STRIPE_ACCOUNT_ID}}',
});