You will be sent a notification each time a payment is made, along with a link to download the associated invoice.
If you would like billing-related emails to also be sent to additional addresses, then you can set this up from your account. Log onto your profile page and enter an email address against the ‘billing email address(es)’ option.
You can also find all of your invoices on your ReadablePro billing page. You can quickly download a new copy, if you need one.