custom commands do not work

You added a "/", which you shouldn't. It automatically does that for you.

If that hasn't fixed your issue, you can try:

1. Removing the spacebar in the text.

2. Using @p instead of player name (If you are referring to players.)

Did you try writing it as: "chestfillmessagefalse" instead of "chestfillmessage false"?

If you haven't solved it yet, you have to have a procedure attached to the command that works in a similar way to this:

So first, the mod element should only have the first word of the command in the "Command Name" slot.  For example, just have "chestfillmessage".

Then, in the attached procedure, drag in the template for "Check command parameter" from the template library.  The basic index value will be 0.  In the equivalent text block, have the desired second word of the command.  For example, "false".

Inside the conditional's "do" portion, have the desired effect of the command.  If you want the command to be more than just two words long, have an identical conditional in this area instead, but increase the command parameter index by 1.  

While this method will allow the in-game command to work with spaces in it, any parameter that is typed after the original command will not autofill.  However, the command will still work.