Some social networks make things easy – there is a clear-cut advertising system on YouTube where Google and many YouTubers share advertising receipts. But Instagram has no such policy. If a firm advertises on Instagram (and parent company, Facebook), all of that payment remains inside Instagram / Facebook. They share nothing with the account holders and content creators.
If you want to earn money from your Instagram activities, you need to take a less formal path. You need to connect with brands – or wait for them to contact you.