Fixes issue 22112 (#22112) by removing shipping address validation from the new billing address form in checkout. It appears this was added initially simply to validate the postcode in the form, but running the billing address through the actual shipping rate functionality in shipping-rates-validator's validateFields function was causing the issues leading to the address disappearing from the Ship To section & being deselected in the Shipping step. Instead, this validation is replaced in the billing address form by a simpler validator which only checks the postcode.

Author: Ryan Simmons

app/code/Magento/Checkout/view/frontend/web/js/model/billing-address-postcode-validator.js

@@ -0,0 +1,83 @@
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+define([
+           'jquery',
+           'Magento_Checkout/js/model/postcode-validator',
+           'mage/translate',
+           'uiRegistry',
+       ], function (
+    $,
+    postcodeValidator,
+    $t,
+    uiRegistry,
+) {
+    'use strict';
+
+    var postcodeElementName = 'postcode';
+
+
+    return {
+        validateZipCodeTimeout: 0,
+        validateDelay: 2000,
+
+
+        /**
+         * Perform postponed binding for fieldset elements
+         *
+         * @param {String} formPath
+         */
+        initFields: function (formPath) {
+            var self = this;
+            uiRegistry.async(formPath + '.' + postcodeElementName)(self.bindHandler.bind(self));
+        },
+
+        /**
+         * @param {Object} element
+         * @param {Number} delay
+         */
+        bindHandler: function (element, delay) {
+            var self = this;
+
+            delay = typeof delay === 'undefined' ? self.validateDelay : delay;
+
+            element.on('value', function () {
+                clearTimeout(self.validateZipCodeTimeout);
+                self.validateZipCodeTimeout = setTimeout(function () {
+                    self.postcodeValidation(element);
+                }, delay);
+            });
+        },
+
+        /**
+         * @param {Object} postcodeElement
+         * @return {*}
+         */
+        postcodeValidation: function (postcodeElement) {
+            var countryId = $('select[name="country_id"]:visible').val(),
+                validationResult,
+                warnMessage;
+
+            if (postcodeElement == null || postcodeElement.value() == null) {
+                return true;
+            }
+
+            postcodeElement.warn(null);
+            validationResult = postcodeValidator.validate(postcodeElement.value(), countryId);
+
+            if (!validationResult) {
+                warnMessage = $t('Provided Zip/Postal Code seems to be invalid.');
+
+                if (postcodeValidator.validatedPostCodeExample.length) {
+                    warnMessage += $t(' Example: ') + postcodeValidator.validatedPostCodeExample.join('; ') + '. ';
+                }
+                warnMessage += $t('If you believe it is the right one you can ignore this notice.');
+                postcodeElement.warn(warnMessage);
+            }
+
+            return validationResult;
+        }
+    };
+});

app/code/Magento/Checkout/view/frontend/web/js/view/billing-address.js

@@ -18,7 +18,7 @@ define([
     'Magento_Checkout/js/action/set-billing-address',
     'Magento_Ui/js/model/messageList',
     'mage/translate',
-    'Magento_Checkout/js/model/shipping-rates-validator'
+    'Magento_Checkout/js/model/billing-address-postcode-validator'
 ],
 function (
     ko,
@@ -35,7 +35,7 @@ function (
     setBillingAddressAction,
     globalMessageList,
     $t,
-    shippingRatesValidator
+    billingAddressPostcodeValidator
 ) {
     'use strict';
 
@@ -66,7 +66,7 @@ function (
             quote.paymentMethod.subscribe(function () {
                 checkoutDataResolver.resolveBillingAddress();
             }, this);
-            shippingRatesValidator.initFields(this.get('name') + '.form-fields');
+            billingAddressPostcodeValidator.initFields(this.get('name') + '.form-fields');
         },
 
         /**