If you want to get a copy of a recent invoice you can do so within Timetastic.
If you're an Admin user, just login and head to SETTINGS > BILLING.
At the bottom right of the page under 'Payment History', you'll see copies of all your previous invoices / receipts available to download.
If you don't see "SETTINGS" in your menu, you'll need to contact one of your Timetastic Admin users to download invoices.
It's also worth noting that you can set two unique email addresses to receive a copy of the monthly invoice, it's covered in the help centre here.