You can access your purchase invoice in two ways as mentioned below
As soon as you successfully complete the purchase we send you your invoice to your registered email as an attachment in PDF Format, you can download this file and use it.
You can login to your account on www.kreatable.com via the login section using your username and password
Go To :
Account --- Profile --- My Account
And then look for the invoice section , you would see all the invoices related to all your purchases, click on any of the invoices ad the invoice would be downloaded as a PDF File and you should be able to use this invoice.