I'm in the middle of this right now. I need a copy of my W-2 transcripts from previous years, the IRS is backed up for the "official" interface to do that, so they want me to pull my own papers manually.
To do that online, you need to create an account. They want SMS verification, but refuse to allow pay-by-the-month plans, so you need to have a postcard physically sent out with a verification code.
(incidentally, the "password complexity verification" was broken on Firefox, even with ublock completely disabled. It required a special character but would never accept that I actually had put one. Also, when I cancelled out and tried it on a different browser it locked me out for 24 hours.)
I just did a "request a copy by mail", that will probably show up sooner than the postcard given that it took another 24 hours to clear the lock and create an account on Safari to get the postcard sent out.