They send you messages (ads) via keysend.

So they pay you for sending you a message:

Satograms are lightning keysend payments that include a custom message. Think of it like spam email, but you get paid for it. When you receive a Satogram you have been paid by the sender! Reach out to thousands of people with your own custom message of up to ~1000 characters in only a few minutes.

-- https://satogram.xyz