Some of the earlier articles from a few months back led me to believe that most of their oil income came from a protection racket they were running on various Syrian refineries.
(nice little refinery you got there,
be a shame if something were to happen to it)
I’ve seen several news articles link the $2 million/day to these refineries. Reporting is so sad these days.
This helps no doubt, but it was likely only a tenth of what income they were bringing in.