How it works
DOPA's help center lays out three steps: the friend taps the invite link, downloads DOPA! and enters the code at sign-up, with phone verification required. The $10 lands for both people after the new user's first purchase, not at sign-up.
Each member can invite up to 20 friends who buy, for up to $200 in credits.
What credits are
Credits buy packs on DOPA and nothing else. DOPA's own conversion option works the same way: an unwanted card turns into credits at 100% of its listed value, not cash. Count the $10 as a discount on packs you were already going to buy.
Before you buy
DOPA is run by sinsa Inc. (dba DOPA!), and its terms let it change the service without notice. Each pack shows its full prize pool and odds, so read them, and the shipping costs, before you spend.