I would just try re-adding it again. Make sure it’s pasted in the correct field. And make sure it’s a lightning address (looks like an email address) and not an invoice. And make sure to hit “Save.” I don’t see the button either in Damus. I see a button in Snort but when I click it it gives an error. Once it’s added the lightning button on posts will work too but you won’t see them in Damus unless youre on TestFlight version.