Buttons such as those are showing up on the sites of nearly 40 nonprofits, courtesy of a new platform called B Generous, which launched six weeks ago. The idea behind B Generous, according to founder Dominic Kalms, is to bring the increasingly popular concept of “buy now, pay later” to nonprofits, which Kalms hopes will enable people to give larger donations than they generally do by spacing them out over time. According to the firm GlobalData, the “buy now, pay later” market grew to $120 billion worldwide last year.