I figure I'd ask since you didn't mention it in your opening post.
There is another topic from someone running 2.20.0 who has no issues installing the firmware. So since 2.3.0 to 2.20.0 work, I would think 2.7 should also work.
Could you specify which regional version of the access point/firmware you have? I know there are issues with flashing the firmware on Canadian models, so perhaps yours also has additional checks that aren't in the "universal" firmware.
To my knowledge, nobody's been able to figure out the root password, or another way to obtain a root shell on these devices.
So I now flashed the EAP225 v3 snapshot done everything like the instructions. After updating the tplink was not reachable on the old ip Adress or 18.104.22.168
Now I restarted my router and the tplink and I don't have a connection via lan on my PC the network named now network 2 so I have no ethernet connection and the TP link is not reachable I cannot even access my router page 22.214.171.124 (Vodafone station a German ISP)
If your default network is 192.168.0.0/24, you router won't know where to send packets meant for 192.168.1.1 (the OpenWrt device).
The OpenWrt device should be at 192.168.1.1 on a newly flashed device, but it will also run a DHCP server. So if your pc requests a new address as you reboot your ISP's modem, you might end up with an address in the 192.168.1.0/24 subnet.
The safest way to set up a new OpenWrt device, is to give your PC a fixed address in the 192.168.1.0/24 subnet, and make sure your PC and the OpenWrt device are isolated from the rest of your network.