You can see your invoices by selecting 'Settings' on your RepricerExpress menu.
If you need to access or print your invoices you can access these inside RepricerExpress. Previous payments will be listed here and you can view an invoice by selecting the appropriate row and hitting the view button. These invoices can then be printed off as you need them.
RepricerExpress will also email you each time a successful or failed payment attempt is made.
Note: if you need to edit your Billing Information (address, company name etc..) you can do it via 'Settings' > 'Billing Info' and this will update all your invoices.