Why Does My Stripe Express Checkout PaymentIntent Report a Missing Payment Method?

I'm implementing a Stripe payment flow that uses both Stripe Elements for card payments and Express Checkout for Google Pay/Apple Pay. I create a PaymentIntent with the following PHP options:

PHPCopied
$options = [
            'customer'                  => $stripeCustomerId,
            'amount'                    => $amount,
            'currency'                  => 'gbp',
            'automatic_payment_methods' => [
                'enabled' => 'true',
            ],
        ];

The Stripe Elements part works perfectly. However, when I add Express Checkout, I get the following error from Stripe:

You cannot confirm this PaymentIntent because it's missing a payment method. To confirm the PaymentIntent with CUSTOMER_ID, specify a payment method attached to this customer along with the customer ID.

I initialize Express Checkout as shown below:

JAVASCRIPTCopied
const expressCheckoutOptions = {
            buttonType: {
                applePay: 'order',
                googlePay: 'order',
            },
            layout: {
                maxColumns: 1,
            }
        }

        expressElements = stripe.elements({
            mode: 'payment',
            amount: Number(window.payment.payment_amount),
            currency:'gbp',
        });

        const expressCheckoutElement = expressElements.create('expressCheckout', expressCheckoutOptions)
        expressCheckoutElement.mount('#express-checkout');

Then, I confirm the payment with this code:

JAVASCRIPTCopied
expressCheckoutElement.on('confirm', async (event) => {
            const {error: submitError} = await expressElements.submit();
            if (submitError) {
                showMessage(submitError.message);
                return;
            }

            let clientSecret = 'Our Client Secret'
            const {error} = await stripe.confirmPayment({
                expressElements,
                clientSecret,
                confirmParams: {
                    return_url: window.location.href,
                },
                redirect: 'if_required',
            });

            if (error) {
                showMessage(error.message);
            } else {
                console.log('Payment confirmation successful!');
            }
        });
    }

This integration closely follows the Stripe documentation (https://docs.stripe.com/checkout/one-click-payment-buttons?payment-ui=embedded-components), but I still get the missing payment method error. I'm looking for guidance on how to resolve this issue—either by ensuring a payment method is attached to the customer before confirmation or by modifying the PaymentIntent creation to avoid this requirement. Any help is greatly appreciated!