Commerce is something of a challenge for social networks to implement, but a third party that has already made it work on Twitter is now looking to expand into other markets.

Chirpify today announced that it will extend its in-stream payment system to photo-sharing app Instagram. With a PayPal account and the right hashtags, users can now buy, sell, donate, or make a payment without leaving Instagram.

Currently, 40 percent of the world’s top brands are on the photo-sharing app, which is currently owned by Facebook. With this application, brands can set up a product listing with the phrase “@Chirpify $amount” and ask customers to reply to their ads with the word “buy.”

“Today Chirpify took another step to decentralize commerce and payments across all streams from any device, whether a mobile phone or desktop computer,” said Chirpify CEO Chris Teso in a statement. “If people can’t buy it in-stream it’s not social commerce. It’s advertising.”

Chirpify also has a number of celebrity launch partners, including tattoo artist Kat Von D and Invisible Children, the creators of the KONY 2012 campaign.

The PayPal connection works for a lot of other kinds of payments, like charitable donations and payments to friends or family members. Digital communications agency Lovesocial, for example, works with Chirpify to help other organizations and charities meet their fundraising goals.

But e-commerce seems to be the main selling point. Added Teso, “We turn attention re-routing advertising into high value in-stream transactions. We’re the only company truly doing social commerce.”