Trouble modding a game " TruMate - Virtual AI Friend "

[phenix60]

hi
i try to mod this game named " TruMate - Virtual AI Friend "
(not sure if i can leave a link to the google store page but here it is, i'll remove it if it against the rules https://play.google.com/store/apps/details?id=com.aichatbot.aimate&hl=en_US )

So i'm trying to get max gems or what they call in the app " pieces" using GG
i found a code apparently which change the value in game as seem on the 1st and 2nd screenshot, but when i exit the page of the gems " piece in game " the value go automaticaly back to how much it was before being modified , like we can see on screenshot 3, and as i starting today to use Game guardian, i don't know why this happen and how to fix it , if someone could help me figuring what happen and how to fix it, i would be really happy.