Roslyn dynamic lambda compilaton and execution

I need some help in understanding about Roslyn (i am new about that technology). In my scenario i have a set of rule, each rule is a string that contain the text of a lambda expression; each lambda take an object as input and get a string as output.

Rule example :

obj => obj.ToString()

My goal is to compile each lambda once (at program startup) and then execute it with the different parameter i get (a runtime) each time.

So from what i have read i think i need to start compiling the lambda first :

            foreach ( var rule in rules )
            {
                //_formattingRules -> a dictionary that will hold all compiled lambda
                if ( string.IsNullOrEmpty(rule) == false && _formattingRules.ContainsKey ( rule ) == false )
                {
                    try
                    {
                        var currentOption = ScriptOptions.Default.AddReferences(property.PropertyType.Assembly)
                                                                 ...other refereces;


                        var script = CSharpScript.Create<Func<object, string>>(rule, options: currentOption);
                        _formattingRules.Add(rule, script);
                    }
                    catch (Exception err)
                    {
                        //error handling
                    }           
                }
            }

Then when i need to use a specific rule on object :

                    if (_formattingRules.ContainsKey(rule) == true)
                    {
                        var currentRule = _formattingRules[rule];

                        if (currentRule != null)
                        {
                            string formattedResult = currentRule.DynamicInvoke(new object [] {objectToFormat});
                        }
                    }

The problem is that when i do so, the DynamicInvoke throw a TargetParameterCountException and that let me think i am invoking the wrong thing. So i belive there is something in my understanding of how Roslyn work that is faulty, and i would like help to figure it out how to achieve a compilation first (once) with multiple execution (different parameter) of a lambda expression.