When you first sign up to the Grifin app, there is a pop up that appears on the "Create a strong password" screen of our new member sign up flow. Just type in / paste your friend's referral code in the box to claim it! Make sure the spelling is correct.
It looks like this:
There is nowhere else to claim this code in the Grifin app, so please be sure to take your time through the sign up process so that you don't miss this referral code claim screen!