Short version. Free for life. One link per placement. The reward lands in your wallet the moment a sign-up is counted, and you keep all of it.
Reels, stories and the link in bio
Instagram gives you a link in bio and a link sticker in stories, and a reel that can point to both. Each of those is a placement. Shopmycode gives each placement its own link, so you know whether the story sticker or the bio link is doing the work, and pays the reward the moment a result from either is counted.
The story sticker is the fastest path (one tap, inside Instagram), the bio link the slowest (tap the profile, tap the link), and the reel the widest (people who never saw your profile). Each behaves differently for each brand, and the only way to know which to lean on is to give each its own link and read the numbers after a week.
Opens from Instagram look different
A tap inside Instagram opens the page inside Instagram's own browser. The live view shows that: 'Instagram app' rather than 'Safari'. It also shows the city and whether the person is still on the page. When your link is forwarded from a DM into WhatsApp, the opens show up as WhatsApp; that is your reel travelling.
What to put in the story
The link sticker with the ready-made message the offer gives you, and the reward if the brand allows you to mention it. Keep the landing page the brand chose; do not route through your own page unless you are tracking that too.
Building a rate card from your own numbers
Results per placement, over a few campaigns, is the number a brand will pay a fee for. Share your Shopmycode numbers with a brand when pitching (you can invite them to see a link's numbers, and they see exactly what you see).
Money
Free for life; no percentage taken. Rewards in the wallet on result, withdrawal by UPI or bank, reversals visible with reasons.