Edit: important, ingame visit the Hollvania Mall and go where Arthur is and click on the phone right behind him (should be active the ‘hang out’ option).
Also don’t forget to go behind there stairs where you can find a hole in the floor that leads to a vending machine, click on it for a Drippy glyph.
Then login on the Warframe website and go here:
https://www.warframe.com/1999/doktorentrati
(You should be able to click on the end option)
and enter this codes with the same order
HOHHLKLLKOKO OHLKKOOLLHHK
KOOKLHLKOHLH OLOKKOKLHLHH
LLOHLHKKOOHK LKLOKHHOLHOK
This will give you a code for a poster ingame
OP forgot a few important steps.
You gotta be logged in the warframe site for this to work. You have to go to ingame hollvania mall and hang up the phone behind Arthur. Then the END button wont be disabled anymore, and you can click it and then you have the fields to input the codes.
Thanks, honestly I didn’t even know that because when the Hollvania Mall was up I explored it and clicked everything, thanks for the info, I’ll add them in the front post