The IRS instructions for paying the deferred tax are at the following link.
Note that you can pay online with EFTPS, but not with Direct Pay.
It's possible that it does not show as owed in your IRS account because the first payment isn't actually due until December 31, but that's just a guess on my part.
evidently, Direct Pay is not available at the present time. whether it will be in the future is unknown
see this IRS webpage
The EFTPS requires submitting an application then awaiting a response from the IRS by letter with a PIN that's needed for verification