I believe that the key to earn money with IG is patience and constancy.
I've something around 13.000 followers, on a particular niche (not just "animals" "cars" and similar). It's one year that I'm trying to push it hard, through FollowLiker, shoutouts, exchanges and so on. I've started making money few weeks ago (yeah, after one year).
At my end, I just contact companies on my niche and selling them shoutouts and for me it works fine.