"Flakka" supposedly refers to alpha-PVP, but seeing as how it was made a Schedule I substance in the US over three years ago (and it's been banned in China, where most of it was originally produced), chances are that anything sold as "Flakka" today might not actually contain any alpha-PVP, but whatever cathinone the vendor found easiest to source (ex.: alpha-PHP, N-Ethyl-nor-Pentedrone, N-Ethyl-nor-Hexedrone...)
...heck, for all you know it could be pretty much anything, or even just a total scam (actually, if someone is really selling it as "Flakka", that seems to be the most likely scenario).