Help/Support [Theos] Setting isPremium to true does not affect anything

[ubyt3x 187 iPhone 15 Pro Max 18]

Our school uses an app called Untis (Germany) which manages students lessons, teacher substitutions and attendance controls. It has an premium option which unlocks the features of viewing days that the teacher marked you as missing for, using the widget (3D Touch and a notification centre widget - without premium it just displays the text "Premium needed") and more.

This app is my first app I'm getting used to Theos and hooking with and I think I can learn from it. It is a simple app and I debugged it several times with FLEXible, I don't know how much of it is server-sided, as FLEXible reveals that just the school broadcast message and the timetable gets loaded from the server, but there are no requests being made that receives information about the user - even requesting the timetable is not protected with a password.

So I started with basic things - changing the teachers name, creating a information text for the lesson and stuff. But my main goal is to get premium working.

This is my current Tweak.x: https://pastebin.com/jrDPQRUB

Setting isPremium along other properties to true sadly doesn't affect anything, but FLEXible shows me instance variables that I would like to change to true as well, that - I think - could lead me to achieve my goal, but I don't know how to hook into an IVar. I searched for good explanations, but couldn't find one.

I hoped that I could get some insight here, which I would be really thankful for.

Heres the iTunes link to the app: https://apps.apple.com/de/app/untis-mobile/id926186904 - It's an swift app.

I thought of maybe that a server-sided request overrides my hook, could something like this be possible? Or is my hook on isPremium completely wrong? I also tried it with YES and NO.

Thanks!