For Damus, I wrote a nice explainer:

How to enable zaps?

If you're on iPhone, then as of today, you may still need to use the Damus beta app, which you can download from the TestFlight app if you have an invitation code. There are only 10k beta slots, so if you don't already have an invitation, you're out of luck for now. But zap support will pop up in the regular AppStore soon.

If your Damus version does support Zaps, then here's how to set you up for zapping:

go to your Damus profile, then Edit, and put an LNURL into the "Bitcoin Lightning Tips" field (LNAddress/LNURL both work I think).

You can get an LNURL from the Wallet of Satoshi App (may need to download it first). Go to "Receive", then hit the "@ Lightning Address" button in the upper right. A QR code will appear. Below the QR code will be an LNURL string. Copy that and paste it into Damus.

Alternatively, you can copy the yellow email address above the QR code. That's the LNAddress. LNURL seems to work best, however, as it's compatible with more wallets. Or so I've heard.

If you're NOT on the Damus beta:

Just keep checking the AppStore version. There will be a zap button next to the "like/shaka" button.

I BELIEVE the current App store version does support zaps now.