Pull the tank lid cover off and make sure that the refill tube from the fill valve is pointed down the overflow tube.
This is what refills the bowl.
If the bowl is not full at the beginning, then the flush from the tank only fills the bowl, it doesn't flush the bowl.
I'm sorry that you installer was clueless.
Yes, you install the adapter with wax, bolts and screws to the floor.
And then you drop the bowl onto that. Most homeowners figure that out pretty easily.
It's too bad that many plumbers don't read the instructions. The paperwork that comes with the toilet shows how much room is behind the tank with a standard 12" rough. You don't have to guess at this.
At 12", you should have 3/4" behind the tank.
The next step after "reading" that, is to use a "tape measure"
The two tools your plumber should have used were
The rest is common sense.
An adapter installed on tile using the green inserts and the screws that come in the Unifit Box.