Help! Hooking

[Baba44]

public void InitiatePurchase(Product product, string developerPayload) { }

How can I hook this method also this is in-app purchase hack offset method

 

[fshn06]

void old_InitiatePurchase(void*, void*, MonoString*);
void hkInitiatePurchase(void* instance, void* Product, MonoString* developerPayload) {
    if (instance != NULL) {
        // ur implementation
    }
    old_InitiatePurchase(instance, Product, developerPayload);
}