Issues with flashing DD-WRT on a TP Link Archer C9 v4 (a.k.a. Archer C1900)

I’ve been postponing this update for a while, just waiting for the warranty to expire on my C9, and i casually remembered doing this today since the stock firmware on the router messed up and deleted the previous settings.
Well, i already run a secondary router (D-Link DIR-868L) as a wireless AP with DD-WRT and it has been working very well for over a year and a half, i’ve been thinkering around the web and i recently i found this article that i wanted to try out, and for that i also need to flash DD-WRT on my C9.
I’ve been trying to pick the files from here which seems to be correct, but all i get when i try to flash this file is an “unable to upgrade” message on the UI.
I did notice one thing about this, my C9 is an american model which has a larger sized stock firmware in comparison with the one DD-WRT provides, which itself is similar in size to the european stock firmware.
Could that be the reason for me not being able to update the firmware?
I tried multiple versions as well, just to make sure and the same thing happens.

Update: So far i’ve tried everything that was reported on the DD WRT forums and wiki to flash this thing and i’m still not able to do it, i still think it has something to do the hardware version.

Update, in case somebody stumbles on this thread in the future, here’s the reason why this update didn’t work.
Guess i’ll poach another router now.