Paypal Checkout Button is not passing custom filed to IPN message

Question

I'm updating the PayPal system on my website, replacing older PayPal buttons with newer PayPal Checkout, and I have problems while trying to pass the custom field from the button script to the IPN message that I use to update my database with customer's payments: I receive the IPN message with all the rights $_POST fields/values, except for the $_POST['custom'] field that always remains empty. I'm using sandbox merchant and customer accounts, this is my button code:

<script src='https://www.paypal.com/sdk/js?client-id=xxxxx&currency=EUR' data-sdk-integration-source='button-factory'></script>
<script>
paypal.Buttons({
    style: {
        shape: 'rect',
        color: 'gold',
        layout: 'horizontal',
        label: 'pay',
        tagline: true
    },
    createOrder: function(data, actions) {
        return actions.order.create({
            purchase_units: [{
                amount: {
                    value: '1'
                },
                custom: '35627187'
            }]
        });
    },
    onApprove: function(data, actions) {
        return actions.order.capture().then(function(details) {
            alert('Transaction completed by ' + details.payer.name.given_name + '!');
        });
    }
}).render('#paypal-button-container');
</script> 

Answer 1

Replace with custom_id, as documented in the Checkout Orders API reference for a purchase_unit

custom will be ignored