Enable a two-factor authentification through PS/Discord, allowing people to prove they are a unique individual.
WHY? - Content promotion. With most smaller based MMORPG's in the 2000's++ we used invites as a way of promoting the game, the invite system has a reward system as part of the marketing. When invitee 1 reaches level 10/25/50, the Inviter, and Invitee get something special as a way of helping grow the game.
Inviter gets growing rewards from invitee 5/10/15/20 ect.
I personally think that faction based "drip" would do fine here, as well as some souls and berries. The level 50 could be enough diamonds to do a exp boost.
WHY2 - you want the users to have unique players behind them, this prevents market flood of the give-away items. Nobody is trying to buy $40 phones and $35 phone cards to get $10 of give-away items.
How does this grow our community? This will give reason for players to invite players. Word of mouth is the best advertising.