Without wanting to pile on the whole ACA/Healthcare.gov morass, I thought this NYTimes article is very insightful "How Healthcare.gov Was Supposed To Work, And How It Didn't". It takes you through a sort of interactive flow chart, indicating a frankly astonishing number of failure points.
With new health insurance plans scheduled to begin for many people on Jan. 1, insurers are worried that repairs to some of the so-called back end systems of the federal health exchange website may not be completed in time. One of these critical systems is supposed to deliver a consumer’s enrollment information to insurers. And the system which the government will use to pay insurers the subsidy portion of a consumer’s premium had not yet been built as of the end of November.(Emphasis mine)