Universes
Tell FlexViz which universes the show has, and it reports every fixture patched outside them. Until you do, nothing is checked.
Declare the universes
Open the project settings with the gear in the header, or File › Project settings…, and stay on the General tab. Type the universes into Universes in use, separated by commas: 1, 2.
Universes are numbered from 1, as on your desk. The first universe is 1, and its first address is shown as 1.001.
⚠ An empty list switches the check off. Empty means "not configured", not "nothing is allowed". The hint under the field says which it is: Leave it empty and nothing is judged — which is the case now, or currently 1, 2.
What is reported
Once the list is filled in, every fixture patched in a universe that is not on it is an error: Universe 2 is not in this project. Click the row to select the fixture.
Usually it is one of these:
an import from a bigger show, with fixtures patched further up;
a Repatch with Continue into the next universe that ran out of room;
a typo in the inspector.
Fixing it
Repatch the fixture into a universe on the list. Or, if the show really has that universe, add it to the list.
On the console
Put on the list what the console show has. A console may refuse a file that uses more universes than its show: MagicQ reports address out of range for a fixture in a universe the show does not have. Set the number of universes in MagicQ first (Setup › View DMX I/O › SET NUM UNIVERSES, then restart), before loading the show.
The list is a project setting: it applies to every scene in the project and is the same for everyone on it. See Settings and where they live.