Oh yeah. I should’ve provided an explanation. It basically allows asking a Lightning provider if an invoice has been paid or not.

For example, on an e-commerce website, I can use bullish@getalby.com to generate an invoice and then check with the Alby servers to see if that invoice has been paid. Once payment is received, I can then send the customer to a thank you page.

Hope that helps.

You can check out the details in LUD-21.