@Tom3171 @Linda108 I don't know if the split payment option is offered to guests on a long term booking- I would suspect not, since the long term policy seems to be set up to ensure guests can't just cancel after holding a host's calendar hostage for a month or more and expect to get a refund.
But either way, the split payment option isn't something a host has any control over, nor something a guest can request of Airbnb, as far as I'm aware. It is either offered to them as an option, or not.
What Airbnb's criteria for offering it or not, I have no idea. How far in advance a guest has booked is likely a criteria- if they book for a check-in in 2 days, I don't think they'd be offered that.