Apple Pay payment sheet won't open

I'm trying to debug Apple code example to open the payment sheet. Yesterday it worked and the payment sheet opened, but today I think I can't pass the session.onvalidatemerchant stage. When I debug, it won't stop in the getApplePaySession(event.validationURL) and instead will jump right to the session.onshippingmethodselected (which doesn't make sense because the light-box wasn't opened yet, right?!).

I don't have any error in the console. "Validate merchant" is not written to the console. This is the JS code Apple provided and which i'm using:

const session = new ApplePaySession(1, paymentRequest);

/**
* Merchant Validation
* We call our merchant session endpoint, passing the URL to use
*/
session.onvalidatemerchant = (event) => {
    console.log("Validate merchant");
    const validationURL = event.validationURL;
    getApplePaySession(event.validationURL).then(function(response) {
        console.log(response);
        session.completeMerchantValidation(response);
    });
};

/**
* Shipping Method Selection
* If the user changes their chosen shipping method we need to recalculate
* the total price. We can use the shipping method identifier to determine
* which method was selected.
*/
session.onshippingmethodselected = (event) => {
    const shippingCost = event.shippingMethod.identifier === 'free' ? '0.00' : '5.00';
    const totalCost = event.shippingMethod.identifier === 'free' ? '8.99' : '13.99';

    const lineItems = [
        {
            label: 'Shipping',
            amount: shippingCost,
        },
    ];

    const total = {
        label: 'Apple Pay Example',
        amount: totalCost,
    };

    session.completeShippingMethodSelection(ApplePaySession.STATUS_SUCCESS, total, lineItems);
};

I solved the problem. The Mac and iPhone weren't configured with the same iCloud user.