Its not true (well, thats a strong statement.. lets say they are not giving you the entire picture). There are plenty of people, many on this very board, who have no powerwalls and see power flow in the app. There are others who (like me) did not see power flow in the app until I got powerwalls.
The reason you dont see it is because they didnt install a device called a "powerblaster". the question is, why didnt they tell you they didnt install it, and what was the reason for that? I would push them to come back and install it, but know they may not do that.
I would recommend being "politely insistent", especially if you have not paid for the system in full yet, saying that you expected the power flows in the app, and are aware that you need a device called a power blaster installed, and that does not require powerwalls to work.
I also would be contacting your advisor or the energy support line if you can, vs email where its fairly easy to get ignored.
good luck! Let us know how it comes out.