I see that people are being told that there is no way to attach a document or explanation to TurboTax and file electronically. I had the same problem. There is an "ACA explanation form." Why that and no other explanation forms who knows, but that's what we have to work with. I was required to attach a QBI aggregation explanation, and TT did not permit me to type it in on the QBI form where it was requested, so I put in on the ACA Explanation form, and explained what it was. I hope it will be acceptable to the IRS. If TT can create an explanation form for ACA, why can't create a miscellaneous explanation form?