The subscription went through on its own, without my involvement!
When registering I chose a free account. Then after a while a window popped up in the app to enter the password for the Apple id, I thought it was just a verification and entered the password, but then I got an email invoice for a full ultimative subscription of 4100¥!!! I didn't subscribe to it, the app cheated me! Also, on my other device in this app, the price for the ultimative subscription is 2000¥! Please cancel the subscription and refund the money!