Unity Tiny, playables for UnityAds

Hello,
I'm using Unity 2020.1.17 with Unity Tiny and I'm trying to make my playable work on UnityAds. And I can't make it work, I'm calling mraid.open on my button but I'm getting an error on the playable in ad testing application "Script Error". But when I am testing on my browser i'm only getting the error when i click on the button (That's normal).
I'm using this js script to call mraid.open on a button (It's working for Applovin):


In my C# script where i detect the button i use:



In the giudelines to make a playable on Unity Tiny i saw that you need to do the bootstrapping of MRAID but i don't know where to do that:



Edit:
I didn't find the .utproject file in the inspector when i followed this thread:
https://forum.unity.com/threads/how-to-use-ads-in-project-tiny.598900/
2nd Edit:
Im calling the bootstrapping function now in a js file in the folder prejs~

but now when i test the playable alone on Unity adTesting it's working fine but not with a video before (error message: "Script Error"). Does the error message come from the application or from my playable

 

I am running into the exact same problem.
When I try to play a playable with the "Video & Playable end card" in Unity Ads, I get a "Script Error".

Has this problem been resolved since then?