Every Elastic Email account stores the history of payments made for their Elastic Email services on the My Account>Billing>View>Payment History screen:
If you click the three-dot menu besides a payment you are interested in, you will be provided with options to "Send Receipt" or "Get Receipt".
"Send Receipt" will send the receipt to your account's main email address.
"Get Receipt" will allow you to download the receipt directly into your device.
Please note that due to the nature of our service we do not provide invoices as proof of payment. Our receipts include all the information required for accounting purposes, including a Tax ID.