Server crashes when plugin loads apparently due to a command

The server crashes every time it loads the plugin it says that the onCommand method must match onCommand in CommandExecutor my code is

PHP:

public function onCommand(CommandSender $sender, Command $cmd, string $label, array $args){

     //Etc

}

i dont see how it dosent match am i doing something wrong with plugin.yml or whatever?

 

Theres such a thing in PHP now? Ah well, thanks

 

PHP:

public function onCommand(CommandSender $sender, Command $cmd, string $label, array $args): bool{
// etc
return true; // change this to whatever , it doesn't have to be (true)!
}

 

Its already solved, but thanks anyway!