Just type a hidden message, choose an emoji and copy the emoji at the bottom and paste into a messenger or Nostr client.

If you want to hide ecash, then you need a cashu wallet and you need to figure out how to get a text copy of a cashu token. It would look something like:

cashuBpGFteCJodHRwczovL21pbnQubWluaWJpdHMuY2FzaC9CaXRjb2luYXVjc2F0YXSBomFpSABQBVDwSUFGYXCCo2FhCGFzeEA4MWNjZWY3NTEzNThjNmMzMTliNDViM2YyOWRhYWJiYTVhMmUzNzkyZWRlZjNkYzdlNDlkZjEzODdjMTdmMGJjYWNYIQKoNeORI9H1y74S6WpbSFuL-4Zsw3J4eXUBq7tZKBXw_6NhYQRhc3hANjQzNmU5OTQyNTM2NDA1Y2Q0ZmJjOGI0YTNkYTk2ZTYxZmM1NDRkNTg1YzM0NjA2NDNhOTExNGRiNTVhYzIyM2FjWCED7ckF-gPbUgvI1ztUP2WvbjDsmGc0dPMNTcrWRaGlOQdhZHJTZW50IGZyb20gTWluaWJpdHM

Use that as the secret message and now you have ecash hidden in an emoji 👍