Mixer is Microsoft's game streaming platform, and the service is always finding new ways of monetization for its partners. Beforehand, only "Sparks" were used to provide patronage to certain channels, but that's changing today with the introduction of "Embers". Embers are a virtual currency — essentially cosmetic microtransactions — that you can give you a popular streamer of your choice to pay them.
Mixer issued the following statement on its website explaining Embers and how they work. The company went into great detail on how they're different from Sparks.