Why couldn't Schacht use all the money they got from MEFO bills?

In TIK’s youtube video How did Schacht's MEFO Bills work? Were they inflationary or not? - YouTube, he mentions at 6:36 that due the MEFO bill arrangement they raised 12 billion reichmarks and they were able to put 6 billion reichmarks in circulation.

I don’t understand, how? They gave you a 4% interest and the government could use the money, so why couldn’t they use all the 12 billion reichmarks?