This makes “park”, not “800” the parkext.
If you include parkedcalls correctly, the parkext will be usable without having to explicitly invoke Park, but if you do, you will get the default options.
It certainly used not to be the case that you needed a callable parkext at all to use the features code for parking, but I suppose it could have changed.
You almost certainly do not want to continue with reparking when it times out, but that is what your c parameter seems to be doing.
The button lighting up is purely local behaviour in the phone. I presume the button simply sends the feature code.