I have stumbled across a possible solution to this problem. I was trying to enroll my 21 year old as part of our plan (so the whole family can share the same very large deductible) and the site also would not allow it. Spent an hour and a half on the phone til they figured out that it wasn't allowing me to enroll because she plans to file her own taxes next year (2020). Once we established that I thought it didn't make sense because she also plans to file her own tax return this year (2019) and we bought a plan as a family for 2019, BUT in November of last year we planned to claim our daughter as a 2019 dependent when we were filling out the ACA application. She is a dancer and part way through 2019 she got a full time gig that greatly increased her income. I asked our accountant and she said we can't claim our daughter on taxes in 2019 because she made too much, but everything is fine since she's still considered part of our "household" for health insurance purposes.
Basically I don't think the healthcare.gov system can handle this particular situation even though we have the right to include our child under 26 even if they are not a tax dependent. When I realized this I asked the Healthcare.gov supervisor on the phone and she denied that their system was wrong. Then I said, so should I just put down on the application that I WILL claim my daughter as a dependent and then not claim her again (as I did for 2019)? And she said I have to speak to an accountant. It wouldn't be dishonest because we don't know if she'll get the same contract next year and if she doesn't, her income will probably be very low and we could claim her. It's complicated when you're self-employed and the ACA doesn't penalize you if the situation changes beyond paying back any subsidy you used if you under-estimated your income. Anyway, you might want to ask an accountant, I'll be double checking with mine but considering that's what we did for 2019 and she said it wasn't a problem, I don't see why we can't do it for 2020. Everything gets synced up when you file taxes in the end.
