Detect API source

Can anybody advise me where this agencies property feed comes from for "new developments"

https://one-marbella.com/en/development/view/1/

I'm sure their listings are from some API feed; however, I don't know who they get their feed from. I would like to find out, but I phoned them, but they won't tell me :-(

Above is the link to the page and listings feed. Is there any way you can tell me who supplies the feed?
Thank you