To send Lightning BTC please follow these steps:
Please note that static Lightning addresses and QR-codes are not yet supported.
In your Relai app, navigate to -> (+) -> Send.
The recipient must generate an invoice in his/her Lightning app/wallet.
Now scan the QR code of the invoice or copy the entire Lightning invoice into the 'Add address/Invoice' field below.
Click on 'Next'.
You now see an overview of the Lightning transaction.
Click on 'Send now' to send the transaction.