func: function addReferrer(address referrer) external restricted {
          if (players[tx.origin].referrer == address(0) && players[referrer].tickets >= interval && referrer != tx.origin) {
              players[tx.origin].referrer = referrer;
              players[tx.origin].checkpoint = players[tx.origin].tickets;
  
              emit ReferrerAdded(tx.origin, referrer);
          }
      }