In the past, you have not been able to buy fiat via ShapeShift. Now, with the ShapeShift Beta, our U.S. users can utilize their ACH bank account to purchase BTC, ETH, and DAI.
To offer this method of on-ramping your crypto, we use an API service called Wyre. When you verify with ShapeShift, you have not yet verified with Wyre, so if you would like to buy crypto with USD, you will have to verify with them as well.
If you are having trouble with your USD-to-crypto exchange, please contact Wyre at firstname.lastname@example.org.