Instance Sync Problem

Hi im having a problem in my game
i created a damage indicator the base damage is 12
but the problem is when i increase my damage the updated damage cant see to the other player
it shows the base damag which is 12

that is the sample code
var ii = instance_create(x,y,obj_damage_indicator);
ii.damage_str = pow;
gms_instance_sync(ii,is_extended | isc_local);