How did the US government get away with not only not paying people for lunch, but REQUIRING them to take one?

Every day you're required to show up for any additional 30 minutes you aren't paid for… and no… you AREN'T allowed to take it at the beginning or the end of the day. https://www.opm.gov/policy-data-oversight/pay-leave/work-schedules/fact-sheets/lunch-or-other-meal-periods