I don't think Iris does zaps, the ⚡ icon is just a lightning: link that opens your wallet (like Alby or whatever) to pay to some LN address.
Zaps have a particular protocol, NIP-57: https://github.com/nostr-protocol/nips/blob/master/57.md
Discussion
Here is a screenshot and i have the ⚡
Yes, I'm typing this on iris right now. The icon next to the heart is just a link to open a Lightning wallet, it is not a NIP-57 zap. Some apps (Damus & Amethyst) implement NIP-57, which is slightly different.
This is separate from, at the moment IIUC, the zaps in those apps are fixed amount 1000 sats.
Ah ok. I'm in amethyst and it defaults to 1000. Appreciate it
it's getting late, I'm not fully reading the post before I reply 🤦♂️