Expression Error in Validif

[Rifad]

I have an expression in ValidIF. It works when I TEST it but returns nothing the app.

I contacted support and they told "Valid if only check the output but doesn't returns a value." 

"It is just to check whether the value is matched with the condition or expression."

"With drop downs it's different scenario."

So I had to send him help documentations so that he can understand appsheet can return as Yes/no,List. 

Then support told me they will look into the issue and contact me back and closed the chat. Does anyone know If i am doing it right ? Looks like a bug to me if I am correct.

Here is my code

SELECT(
			Product Bill of Materials[BOM Product ID], 
      
      IN(
        [Product Bill of Materials ID], 
        SPLIT(
        SELECT(
        			Sales Order Acceptance Items[List of Bill of Materials],
              [Sales Order Acceptance ID] = [_THISROW].[Sales Order Acceptance ID]
      
     				 ), " , " )
      	)
	
  		)