Man, I see this question a lot and I get the impulse, but I gotta be real: you're not gonna find a legitimate way to get the full 'Divine Rivals' audiobook for free in a downloadable, offline way. Audiobooks, especially from a major publisher like Macmillan, are treated just like the physical product. That production cost is huge, with narrators and everything.
You might find those sketchy sites that claim to have MP3s, but half the links are dead or lead to malware. More importantly, it takes money away from the author, Rebecca Ross, and the whole creative team. The actual path for free is your public library. Apps like Libby or Hoopla let you borrow the audiobook for free with your library card. You can download it for offline listening during your loan period. Wait times can be long for popular titles, but it's the real deal.
I just put a hold on it through Libby myself; says it's a 6-week wait. Better that than dealing with some janky site asking me to complete ten surveys.