If you are referred to MISTPLAY by a friend, you'll get a bonus of 50 units for signing up with their invite code. Entering an invite code is very simple. After downloading MISTPLAY you will be prompted to sign up, either with your email or by signing up with Facebook. As soon as you enter your information you will be prompted to enter an invite code (shown below)
After clicking "done", if your invite code is valid you will get the following notification.
That's all there is to it! You are now registered and 50 units have been automatically deposited into your account.
Unfortunately, if you have already signed up for a MISTPLAY account, you can no longer enter a referral code.