To download your invoice, please log in to your online account at gails.com with the same email you used when you placed your order.
Once you're logged in, head over to the 'orders' section of your account. You'll find a list of all your past orders there. Find the order you want the invoice for and click on it to see the details. You will find a button to download the invoice.
Additionally, you can download your invoice right after you finish your purchase, after the checkout page.