Hi… It looks like you might be running an old version of flyctl.
(Perhaps installed via one of the optional Windows package managers, 
.)
That field was changed from bool (which it’s asking for) to string (which you have) some time ago, in order to accomodate the new suspend feature.
It would be best to upgrade at this point—but if that’s not actually feasible then you could try changing 'stop' to true.
Hope this helps!