All in-app purchases in War Robots are processed via iTunes. To see a list of the purchases, view your iTunes & App Store purchase history:
On your iPhone, iPad, or iPod touch:
Settings → Your account name (Apple ID, iCloud, iTunes & App Store) → Media & Purchases → Purchase History
In iTunes (PC/Mac):
iTunes → Account → View My Account → Sign in with your Apple ID → Purchase history → View all
On Web (this will show purchases made over last 90 days only):
Go to reportaproblem.apple.com → Sign in with your Apple ID → Select the 'Receipts' tab
Read more about how to view your iTunes & App Store purchase history: https://support.apple.com/en-us/HT204088