So, the easiest way to implement showing a spinner in a dynamic action is as follows.

 Dynamic Action  	1. Execute JavaScript Code 	popup = apex.widget.waitPopup(); 	 	2. Execute Server-side Code 	--your PL/SQL code 	 	3. Execute JavaScript Code 	popup.remove();  

Let’s implement it in Apex. I created a button called btnRun and now it’s time to set up the dynamic action.

Step 1) Execute JavaScript Code

Step 2) Execute Server-side Code

Step 3) Execute JavaScript Code

I hope this helps