That doesn't work all that well on mobile apps, since users first have to download a new app before you can record the referral code. Having a link click persist through that process is nearly impossible.
Make the link go to a web page with a "download app" link -- the app can start and look for a cookie left by the web page.
Or simply download the app and click again.
I'm not saying not to have user-readable ref codes (though emojis are a terrible choice -- you can't read them aloud), I'm saying make typing them the very rare case.
Or simply download the app and click again.
I'm not saying not to have user-readable ref codes (though emojis are a terrible choice -- you can't read them aloud), I'm saying make typing them the very rare case.