Sounds simple enough, but federal officials and insurers are concerned that many consumers don’t realize they have to take this last step and will remain uninsured. What’s more, those who don’t pay by then may have their Obamacare applications terminated, forcing them to re-enroll via healthcare.gov for coverage that will begin later in 2014.

The tight deadline and continuing errors with consumers’ applications being sent to insurers also risk leaving some folks uncovered. Obama administration officials are advising consumers to check with their insurer of choice to make sure it received their application and payment and that coverage will begin Jan. 1…

While the Obama administration has reported that more than 100,000 Americans picked plans in October, the first month of open enrollment, it’s not known how many of them have paid.

One insurer, Physicians Health Plan of Northern Indiana, has received payments from only about 20% of applicants, nearly all using the firm’s online portal, said Jim Brunnemer, the chief financial officer. It is sending invoices and email reminders to those who haven’t yet sealed the deal. If payment isn’t made by New Year’s Eve, PHP has been told by federal officials that it must void the application.