openwrt-19.07.2-ath79-generic-tplink_archer-c7-v1-squashfs-sysupgrade.bin and the checksum matches. I open the gui select the upgrade page. There I uncheck save configs and then browse to the upgrade package. Upon selecting to run the upgrade, I receive a message, in red letters: "The uploaded image file does not contain a supported format". What did I do wrong?
Since you have v2 hardware, use the ath79, archerc7-v2, sysupgrade bin.
I've never had a problem with sysupgrade -n -F. If you use the proper firmware it will work. Note that -F will flash any file without checking at all, so using the wrong file will brick the router. It's also a good idea to run sha256sum and check the sum on the copy in the router /tmp directory just before flashing the file.
If it does brick, you're going to need TFTP like they said in the first place.