I want the player to move a bit to where it's looking at.

            ServerPlayerEntity player = command.getSource().asPlayer();
            Vector3d v3 = player.getLookVec();
            player.addPotionEffect(new EffectInstance(Effect.get(25), 13));
            player.addVelocity(v3.x, v3.y, v3.z);
            return 1;

 

addVelocity() didn't work. How do I use this?

Nevermind, adding this below addVelocity made it work. Sorry to interrupt!

player.velocityChanged = true;