The Internal Revenue Service has announced that Wednesday at 12:00 p.m. ET is the deadline for those individuals to register their children with the non-filer tool on the IRS website. People who filed tax returns in 2018 or 2019 do not need to register on the site.

The reason for the extra step is that while the government has your bank information, thanks to those benefits, it doesn’t know if you have any children eligible for the stimulus checks.

The $1,200 payments to individuals are being sent automatically, but have not yet gone out to benefits recipients. And once the payment has been issued, you won’t be able to use the non-filer tool to add kids, meaning you’d have to wait until next year to receive the cash. (Stimulus payments are formally an advance credit on 2020 tax returns.)

People who receive Railroad Retirement benefits and Supplemental Security Income (SSI) will also have to make the IRS aware of eligible children.

While millions of taxpayers have already received their stimulus checks, millions more have not—and have grown frustrated with the IRS’s “Get My Payments” portal, which has posted vague messages that have frustrated and confused many users.

More personal finance coverage from Fortune:

—What to do if you can’t pay your bills this month
—Stimulus checks are being deposited: 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
—Freelancers and independent contractors can now apply for SBA Paycheck Protection Program loans. What you need to know
—Listen to Leadership Next, a Fortune podcast examining the evolving role of CEOs
—VIDEO: 401(k) withdrawal penalties are waived for anyone hurt by COVID-19

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