Hello. Please use the console command "silentgive.toggle true" either through the server console or through the in-game console(the "silentitemsgive.admin" permission is required).
Also, please check whether the plugin is installed correctly and whether there are any errors. Try downloading and reinstalling the plugin as well.
And what kind of messages are being displayed exactly?
If it is something like "you silently gave...", then it means global notifications is disabled, and only you can see that message.