1. Enter Mammoth Hunters website at http://mhunters.com/a
2. Sign in with your account
3. Go to Settings -> My suscription
4. In case you had an active iTunes subscription cancel it.
5. Choose Mammoth Plan (the regular one at 59.55 USD)
6. Enter the promo code: xmas2016-50USD-MH
7. Enter your credit card data 
8. Click subscribe

You can then log into your mobile app and will have your PRO account activated at 50% discount for 1 year!