Posting from controller to controllers with parameter gives an error public function actionMyPluginActionControllerIndex(){
    $this-&gt;myPluginActionController($myVariable);
    return something;
}

public function actionMyPluginActionController($myVariable)
{
    return something;
}


This is giving me the error:

{"error": "Missing required parameters": myVariable"}

I did exactly this with a craft 2 plugin, but somehow this doesn's seems to work in craft 3 anymore, what am i missing?

any help will be appreciated :)
You receive this error because actionMyPluginActionController expects a variable in it's parameters. You'll have to declare a default value 

public function actionMyPluginActionController($myVariable = null)


or you need to declare something in your actionMyPluginActionControllerIndex

public function actionMyPluginActionControllerIndex(){
    $myVariable = 'foo';
    $this-&gt;myPluginActionController($myVariable);
    return something;
}


Unless you deactivated error messages/warnings on global level (via web config, dev mode off or something else), there is no way this would work in Craft 2 by default