OpenWrt on Actiontec GT784WNV


I'm having trouble flashing OpenWRT onto the Actiontec router.

I tried the stock firmware web-based update (it rejects the OpenWRT bin file) and TFTP. which shows:

tftp -i put install__openwrt-15.05.1-brcm63xx-generic-96328avng-16M-flash-generic-squashfs-cfe.bin
Transfer successful: 8388864 bytes in 13 second(s), 645297 bytes/s

But the stock firmware remains.

I'm posting this in case anybody else has this router and can write some proper documentation.

The wiki was not helpful.

What happens if you try 17.01.6 or 18.06.1 instead of the ancient 15.05.1?