You can view the invoice history for a client both in the Web Portal and the App, via the Contact Management Portal.
In the web Portal go to CRM > Contacts > select the Edit arrow for the desired Contact > select the Accounts icon > select Invoices. You can also filter by invoice status (All, Unpaid, Paid, Overdue).
You can create a new Invoice by selecting the New button in the top right, and selecting Invoice.
In the App, go to CRM > select the Contact > select the calculator icon > select Invoices > select Unpaid, Overdue, or Paid.
You can also create a new Invoice by selecting the + symbol in the bottom right.