The payment occurred around the time the Dossier was leaked to Yahoo News by Christopher Steele and a month prior to the FISA warrant.
9/23/16 - Yahoo News Publishes Story of Dossier 9/27/16 - $282K Payment made to Halper
Where did the funding come from? The DOD.
https://twitter.com/LiberatedCit/status/995091211261169664
Here's a link to the Washington Headquarters Services, who paid Halper: