You need to be Zap enabled
Discussion
I'm using Amethyst, still trying to figure out if it has this feature.
Amethyst is zap capable but you would also need zap capable NIP-57wallet like WoS or ln.tip.
I Also use that app. When I try to zap someone using wallet of satoshi. It only let me send 1000 sats. Do you know how I can modify the amount of sats ?
I use Amethyst with Getalby and that seems to work. Was able to zap myself some Sats 😄