I think the CoinOS removed the option for LNUIRL-w. If I remember correctly it was available in the previous version.

here is a playground for testing LNURLs: https://lnurl.fiatjaf.com/

And here is a real LNURL for testing (10 to max 21 sats)

LNURL1DP68GURN8GHJ7ER9D4HJUMRWVF5HGUEWVDHK6TMHD96XSERJV9MJ7CTSDYHHVVF0D3H82UNV9AFKKDZVF4M9V4JDG4J9QEEEDAQ4XJNSDFSKKT6XGECNXEMTG3HY5JNTFEXNJNZYVEP4J6292Q4S0PGH

or as link
https://demo.lnbits.com/withdraw/GWgSxQEkj7LyNXq8LojkkH

assmilkers, don't bother to drain it, is just a limited demo