The article states that they were previously forced to block Cuban ip addresses and that AirBnb actively lobbied to be allowed to do business there. Also they had to find a way to forward payments to Cubans as most of the banks will not do this.

The article clearly states that they had to jump through hoops to pay hosts, since they all want cash. They did that, as well as a few other things (looks like they had to talk with the US government about it as well first).