Adding ussd service to my app

I created an app that need a subscription service , and so i decided to use ussd service but the issue is i dont even know how to code ussd onto my app.Can i have tutorials and advice on how to implement this service to my app. And another thing is that it is through the keypad of their phone to dial the ussd and not from the app.

Means users have to pay to use some content of your app like pro version of apps.

Yes that is what i mean .

You can use In app purchase component to do this.

it is not in app purchase that i am trying to implement but for them to buy the service through using ussd code by typing on their keypad .

Please provide full information, what you wants to do ?

What I am trying to do is implement ussd service for my app but i want it to be such a way in which the services will not be implemented from my app but through their phone keypad by just typing the ussd code.How do i do that ?

And another thing i will like to ask is that , in order to be able to use the ussd service , must i buy the ussd service before i will be able to implement on my app ?

You have any screenshot available which helps me to understand more ?

what i am trying to vode is that when a person dials *828# from their phone keypad , they automatically join a group . Can that be done and how ?

these are App Inventor blocks and not Kodular blocks…
therefore please ask in the App Inventor community
I will close this thread