try this
void (*addcoin)(void *instance, int value);
void (*old_update)(void *instance);
void update(void *instance) {
if (instance != NULL) {
if (Coin) {
addcoin(instance, 99999);
}
}
old_update(instance);
}
addcoin = (void(*)(void *,int))getAbsoluteAddress("libil2cpp.so", 0x81C4FC)...