There are currently two ways.
If you receive a request for "Sonix clean-up" directly from a team member at Sonix, Sonix will pay you via PayPal. The typical rate for "Sonix-clean-up" is around 50 cents per minute of audio or video. Payment for transcription work performed is made the first week of every month in USD.
If you receive a request from the Sonix Transcriptionist Directory, you will need to organize payment with that new client. You can also negotiate a rate, but the typical rate seems to be hovering around 50 cents per minute of audio or video.