How exactly did you do that? You’ve been posting command options, but I don’t see this one.
Alternatively, you can do it in GUI Settings (assuming one can get in, e.g. using local access).
Note that --webservice-allowedhostnames is (accidentally) the 2.0.9.102 spelling of option
--webservice-allowed-hostnames. The help text for each version shows the correct option, however Windows TrayIcon help is quite troublesome, which is why I suspect CLI start is rare.
EDIT:
Server help works. User manual doesn’t document either one. Code will change to take either.