Last week i successfully used LP to Cracked Cytus II, but Its process is rather complicated. 

1.First press Buy Songs, then LP will pop up the prompt box and press YES.

2.Then the purchase was unsuccessful and the game was frozen.

3.At this point, you just press the "Settings" button and then exit the settings. You will find that the game picture is back to normal, but the song still needs to be paid.

4.Press the purchase button again, and then select NO in the LP pop-up window. You will see that the song has been unlocked.

I don't know why I need to press yes and no to make the deal work. I hope this problem can be solved.