A press release from the House Energy and Commerce Committee (emphasis added):

Data provided to the committee by every insurance provider in the health care law’s Federally Facilitated Marketplace (FFM) shows that, as of April 15, 2014, only 67 percent of individuals and families that had selected a health plan in the federally facilitated marketplace had paid their first month’s premium and therefore completed the enrollment process. Nationwide, only 25 percent of paid enrollees are ages 18 to 34….

…bThe committee has compiled the data that provides a snapshot of the true enrollment picture as of April 15, 2014, after the official end of the open enrollment period. Due to the administration’s repeated and unilateral extensions and changes, as well as the fact that many insurers have reported that individuals will still have time to pay their first month’s premium, the committee plans to ask the insurers in the federally facilitated marketplace to provide an enrollment update by May 20, 2014.

On April 17, 2014, President Obama declared the success of his law, claiming that 8 million Americans had signed up for health insurance, but data from the insurance providers reveals that the president’s figure is largely misleading. As of April 15, 2014, insurers informed the committee that only 2.45 million had paid their first month’s premium for coverage obtained through the federally facilitated marketplace. While the administration has relied on questionable nationwide figures to boast the law’s success, the state-by-state breakdown compiled by the committee underscores the serious problems facing some states.

For months, the committee and members of the press have urged the administration to provide rudimentary details about enrollment under the law, including information regarding the makeup of the risk pool and who had actually paid for their health care plans. Administration officials repeatedly insisted they were incapable of collating that data and that the insurance providers are the only ones with those details. The committee followed the administration’s suggestion and went directly to the insurance providers.

CBS News points out these numbers are a far cry from those predicted by Kathleen Sebelius:

The data also diverges from the estimate that Sebelius gave in March.

“What we know from insurance companies… tell us that, for their initial customers, it’s somewhere between 80, 85, some say as high as 90 percent, have paid so far,” Sebelius told Oklahoma City CBS affiliate KWTV. However, she noted, “Lots of companies have different timetables for when their new customers have to send their first payment.”