If you have existing sales or purchase documents when the app is installed you need to initiate the booking entries tables. There are two tables, Sales Bookings and Purchase Bookings, navigate to those tables and select Initiate Booking. This needs to be done in each company in the environment.
Note that initiating the booking tables are done on the current date using the current orders, it does not to go back in time and capture prior periods bookings (the data for that does not exists). Although it is possible to import historical booking data using configuration packages.