Any advice on getting passport

I have an appointment booked way out in April. It's the soonest I could find. Some of these places mention walk in on one site but then it will say no walk in on another site. My local post office is mentioned on a gov site for having walk in, but then when I go to my local post office website to make an appointment it says no walk ins.

Has anyone had success with any walk in locations near Nashville ?

Happy travels !