So I've got an unusual version of this problem (I think).
I can get ED working from the desktop icon just fine, but then I'm trying to launch using Dr. Kaii's ED Profiler, and have it linked to the right folder.... but when I try to run it from there it always asks for a code, and when I enter it it says need to register/authorize the account or whatever... and never lets me do it.
I picked up the game on EGS and I also noticed if I open the launcher directly, it doesn't 'see' that I'm entitled to the game, despite linking my Epic account to my Frontier account, signing in, etc. Opening the launcher directly doesn't pass any of the Epic path variables like the EGS launcher would do. It seems the launcher has some built in logic to circumvent the standard ED:F eligibility check for accounts but only if launched from Epic.
Like you, I was also having the same error messages about needing to purchase a copy of the game, and being forced to enter one-time codes which did nothing, despite clearly having the game linked.
Fortunately after a few days of playing, I noticed the game was on sale for almost nothing on Steam, so I picked it up off there - works fine, as you'd expect. A little bit of a shuffle unlinking my EGS and associating my Steam account with my Frontier account, but I was able to do it without Frontier support intervention.
. Return the money.
