I used to use Ivermectin pour on. It's supposed to be put on bare skin on the back of the neck where the chicken's mouth or eyes cannot come in contact with the product unlike under a wing. @afrowoman You are correct in that it isnt given orally, the product contains alcohol among other things.
All this said, I dont recommend using ANY ivermectin products due to worm and external parasite resistance to Ivermectin products, not to mention a long withdrawal period.
If you're going to worm birds, use a benzimidazole such as Safeguard or Valbazen. If you're going after external parasites, use Permethrin liquid or powder.