Invoices are sent to the Adjace administrator that subscribed to a plan. You can find which email this is being sent to in Settings > Subscription and clicking "change" next to the card number on the right side of the page.
This screen pops up where you can see the email. The invoices are sent each month as the account is charged. Make sure to check your spam folder if you are unable to find an invoice. If you need assistance, reach out to us at email@example.com.