The IRS has clarified several reasons on its site that users may get the error message, including:

• They haven’t finished processing your 2019 return
• You entered your data on the Non-Filers portal, but it hasn’t yet been processed
• You receive an SSA or RRB Form 1099 or SSI or VA benefits, and that information has not been loaded onto the IRS systems yet for people who don’t normally file a tax return.

The IRS also added another key point to its FAQs. One reason you could be receiving an error message is that, “The application doesn’t yet have your data; we’re working on adding more data to allow more people to use it.” In other words, the agency is racing to keep up with the massive amounts of information filers and non-filers have been uploading over the past two weeks.

Richard Winchester, a Professor of Law at Seton Hall University School of Law and an expert in federal tax policy says, “It takes time for the IRS to process information that a user may have provided through the web portal designed for people who do not file a tax return.  Until the IRS verifies and processes that information, the “Payment Status Not Available” message will appear whenever the user tries to get an update.”

The agency says it updates the Get My Payment information once per day, overnight, so checking back multiple times during a given day will not be effective. A press release on the agency’s website last week read in part:

“The Get My Payment site is operating smoothly and effectively.  As of mid-day today [April 15], more than 6.2 million taxpayers have successfully received their payment status and almost 1.1 million taxpayers have successfully provided banking information, ensuring a direct deposit will be quickly sent. IRS is actively monitoring site volume; if site volume gets too high, users are sent to an online “waiting room” for a brief wait until space becomes available, much like private sector online sites. Media reports saying the tool “crashed” are inaccurate.”

But Winchester also notes another pain point: Some taxpayers routinely elect to receive refunds via debit cards from their tax preparers, such as H&R Block. But when it came time to send stimulus checks, the IRS erroneously sent their stimulus money to the tax return preparers, Winchester says.  “It’s not yet clear how this situation will be rectified or how long it will take,” he says. “However, people who receive same day refunds from a tax preparer tend to be at the lowest end of the income ladder. So, they probably need the money more than anyone. That means it’s a very big problem if they have to wait to get access to it.”

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Must-read stories from our May 2020 issue:

—How the American economy can recover from the coronavirus pandemic
—Our 2020 list of the World’s 25 Greatest Leaders is dedicated to heroes of the pandemic
—The coronavirus crisis could make Big Oil greener
—For airlines in freefall, the return route will be long and bumpy
—Chart: How each industry is fueling the U.S. unemployment rate
—Everyone is using Zoom, but is that what Zoom wants?
—WATCH: How Seattle’s corporate giants banded together to combat coronavirus

More personal finance coverage from Fortune:

—What to do if you can’t pay your bills this month
—Stimulus checks are depositing: How people are spending the money
—Couldn’t track your stimulus check? Errors and long waits plague IRS portal rollout
—What you should know about mortgage forbearance and skipping payments
—Everything you need to know about furloughs—and what they mean for workers