I’m preety sure this question has been asked MANY times, but no one is giving a answer. I’m using admob and to my knowledge UE4 doesn’t support Interstitial ads through admob. So is there any other way to add it in?
You can use Universal Mobile Ads plugin: Universal Mobile Ads for iOS & Android - Marketplace - Epic Developer Community Forums
Ya, but that costs money. 99$ is too much for me for just Interstitial ads. Sorry.
I think this plugin is worth its price because it’s a complex ads experience for mobile on UE4. 
As soon as you start earn money thanks to the plugin, your investment will return 
If you are willing to delve into C++, you can add support for pretty much anything. Most of my ad support is custom code written by myself and not using UE4s objects at all at this point. If not, then unfortunately you will need to either wait for Epic to add it, get someone to code it for you, or purchase something.
gameDNA, I love what you’ve done with your plugin; it’s really awesome works and well-deserved kudos to you. Honestly, that’s great work and hats off to you. Of course you think it is a great price, but you have to admit $99 is a bit steep for a lot of indie devs who just don’t know if they will make any money back. I understand you may be confident they will and you are saying ‘please trust me’… so why not give him a deferred license and find out? Sounds like that would be a win-win for everyone, no?