Ah I had this in the days when I was living in the tropics… Clay soil, i’m guessing? I had papaya that would grow great during the dry season and then turn yellow and die once it started raining…
I think your soil lacks drainage, or that papaya is planted in a spot where water underneath can’t flow out. Never a problem when it’s dry, but after a month of rain the tree starts rotting from below.
Honestly I think there’s no recovering at that stage, better off pulling it out, digging up the clay soil and mixing it up with lots of loose plant material. Since it seems you’re on a slope, try raising a side with rocks to form a terrace, this will raise soil level higher but excess water can drain out easily between the stones so it won’t rot.