Hello, I’m planning to install OpenWrt on my TP-Link Archer C20 v1 router. I noticed that the links for the OpenWrt Install URL and OpenWrt Upgrade URL are exactly the same. Could someone kindly confirm if this is correct? Thank you in advance!
https://openwrt.org/toh/hwdata/tp-link/tp-link_archer_c20_ac750_v1
You have to prepare special one-time image for tftp (not web ui) by combining bootloader from tplink image and OpenWRT sysupgrade file.
https://openwrt.org/toh/tp-link/archer_c20_v1#using_tftp_method
Try to show files you got before attampting to program the device. Flashing sysupgrade without bootloader over web or tftp certainly bricks device rewriting bootloader with non-bootloader and needing recovery with flash programmer.