I was listening to My First Million podcast the other day and they mentioned a product that was specific to Poshmark, I wonder if this was it. They went on to talk about getting in early to platforms and making a killing (ex. when FB opened their API, Shopify marketplace, Google Ad words). Poshmark seems like a giant service that likely has a lot of area ripe for development.
[1] https://jdnoc.com/open/