It may be that no one uses fluxbox.

According to the documentation:
Example 5-1. A Fluxbox keysfile

Mod1 Tab :NextWindow
Mod1 F1 :Workspace 1
Mod1 F2 :Workspace 2
Mod1 F3 :Workspace 3
Mod1 F4 :Workspace 4
Control n Mod1 n :NextTab

So, as you can see, First there is a modifier, then a key (then a modifier and key again if you wish to have a longer sequence) and finally a colon with an action.

I don't see where you are putting the final colon with an action. For more on this - try fluxbox docs

And please, Read the Rules