To define the invoicing details, on the Admin page go to Billing details (A).
On the settings panel, click Edit then enter the appropriate details. You should make sure to set:
the entity name (B), such as the name of your hospital, so that users can see where their invoices have gone
the email address that invoices should be sent to (C).
it might be important to set the Invoice code (D), for instance if your accounts team has a specific identifier for invoices for on-call shifts.
The other information is optional.