It appears the IRS lacked their direct deposit information, the Treasury, companies and experts said.
The payments, $1,200 for individuals, $2,400 for couples, and $500 for each dependent, are part of the $2 trillion Coronavirus Aid, Relief, and Economic Security (CARES) Act passed by Congress and signed into law by President Donald Trump three weeks ago.
The report said Mnuchin has told the IRS to issue payments quickly to ease the pain of the coronavirus that has shuttered much of the country and put millions of Americans out of work.
But glitches have frustrated some taxpayers, the Post reported.
Over the weekend, the IRS tweeted that the first checks had been direct deposited to bank accounts and more money will be coming soon.
On Wednesday (April 15) , the agency launched a Get My Payment tool to track payments of the coronavirus relief money.
Parents told The Washington Post they received a $1,200 payment for a single head of household or a $2,400 check for a couple, but that the IRS failed to provide the $500-per-child-under-17 payments.
A Treasury spokeswoman told the Post that the IRS processed nearly 80 million payments, or more than half, in less than three weeks.
The glitch comes as the number of workers who filed for unemployment benefits set a record last week, as another 5.2 million Americans applied for jobless benefits, bringing the total to more than 20 million in just weeks.