My understanding is that scratch is really just a treat to be given in moderation, something you toss in the run to give them something to pick at. It is not nutritionally complete, so it would not be healthy for them to eat it as their only feed.
Depending on the age of your chickens, they should be getting either a starter crumble, laying feed, flock raiser, or something along those lines which meets their nutritional requirements.
If they are being picky, I would just provide the feed by itself and not give them any scratch until they are eating the feed regularly.