# in the front-end checkout process,Part 1
* in IDE:
# open `/themes/advanced/in-commerce/elements/content_boxes/checkout/shipping_address.elm.tpl` template for editing
# change `OnUpdate` to `OnUpdateAjax` in it and save changes
* on Front-End:
on "Shipping Information" step,# add a tangible product to the Shopping Cart
change event under "Update Address"# press `Proceed to Checkout` button from `OnUpdate` to `OnUpdateAjax`to go to the `Shipping Information` step
# fill the formall fields, excepting `Zip Code`
# press "Update Address" button
# confirm, that page after reload displays correct JSON data - `{"status": "FAILED","uploader_info": [],"field_errors": {"ShippingZip": "Field is required"}}`
# Part 2
* in IDE:
# revert changes made to `/themes/advanced/in-commerce/elements/content_boxes/checkout/shipping_address.elm.tpl` template
# open `/themes/advanced/in-commerce/elements/content_boxes/checkout/billing_options.elm.tpl` template for editing
# change `OnProceedToPreview` to `OnProceedToPreviewAjax` in it and save changes
* on Front-End:
# fill the missing `Zip Code` Field
# confirm, that page after reload displays correct JSON data - {"status": "FAILED","uploader_info": [],"field_errors": {"ShippingZip": "Field is required"}}# select shipping type
# in the front-end checkout process, on "Billing Information" step, change event under "P# proceed to preview" button from `OnProceedToPreview` to `OnProceedToPreviewAjax``Billing Information` step
# fill the formall fields, excepting `Zip Code`
# press "Proceed to preview" button
# confirm, that page after reload displays correct JSON data - `{"status": "FAILED","uploader_info": [],"field_errors": {"BillingZip": "Field is required"}}`