The alttag is here:
"Product listing: Sunflower - Testing"
This should be enough and is fine. Eventhough the client you are using does not render kind30402 events, it can display that string making it clear what it is, i.e. a product listing, of a sunflower.
Nip 89 integration should subsequently give you the hints as to what clients you could use to render the event, if you are interested.