Hello Mhmd,

Welcome to the community! :)

You can use DFP ads with Interstitial Overlays, here’s a quick guide for you to follow:

1. Create a new Interstitial Overlay by clicking on “+ Add New” or edit an existing one
2. Choose any Overlay Type, I recommend you to choose None if you don’t want any additional content
3. Scroll down to the Content section
4. Switch view from “Visual” to “Text”, like in the following image:

5. Paste your DFP code and then scroll up to the top and click on Save or Update on the top right corner

Hope this helps!