Of COURSE their system is broken! You missed the point entirely.
The purpose of ANYTHING the USPS does is to get you to come to a branch and stand in line. Essentially they want you to be so frustrated and give up that you come stand in line. So they can try to upsell you on stuff you don't want, mainly because you might be weak after spending an hour in line and just agree to whatever is suggested.
This is why the USPS has carefully removed nearly all the stamp vending machines they used to have in every Post Office lobby, why they got rid of the automated mailing kiosks (and those that remain are often broken and simply tell you to go stand in line), and at the same time, they have cut back on the number of clerks working so the line -which you pretty much HAVE to stand in- is as slow and long as possible.
Where a retail store would offer options to customers, open more lines, stay open later in the day or on weekends, the USPS steadfastly does exactly the opposite. The lines are long. YOU HAVE TO STAND IN THEM and forget picking up mail after work. No. You have to take time off. Sucker.
Compare this to Fedex: Their online shipping system is just amazing. And it works. And it's simple. They will come get your package or, at least in town, I can drop it off at their facility as late as 10:00 at night and there's never a line. It just works.
They just added a print kiosk to their lobby so even if you don't have a printer, you can still prepare the entire shipment ahead of time and just scan a QR on your phone to pull up the label, print it, stick it, and done. It's awesome.
The USPS, forget it. I stood in like there yesterday for 40 minutes while the one clerk working argued with a customer about a PO box issue. Nobody opened a second line although there were plenty of clerks standing around behind the counter and a line of customers that grew and filled in behind me, probably 30 deep.
So yes the website is broken. Come stand in line. THAT is your fix. Where is my consulting fee?