FedNow
en.wikipedia.org
en.wikipedia.org
Notable big boys are Wells Fargo, US Bank, JPMC, and BNY Mellon. Also, the US Treasury (“U.S. Department of the Treasury’s Bureau of the Fiscal Service”).
Both counter parties need to be onboarded for the capability to be available.
When can I use it to pay the IRS?
Guess I need to open a bank account with one of these to use it, but would prefer to see something first.
I've made a few pages here and there and it's certainly takes some time to find reputable sources to prove notability and get a decent starting article out.