Command & Conquer Tiberian Twilight - Registration Code

Hello all,

I recently bought "The Ultimate Collection". Everything was fine until now, but when I tried to start C&C 4 Tiberian Twilight the game asks for a registration code before starting. The message also states that: "Your registration code can normally be found on the back of your game manual. If you purchased this game digitally, then your code may have been e-mailed to you" 

Since I own the digital version, the advice "back of my game manual" cannot be used. At most, I received a confirmation of payment and a list of games in the given edition by email. No registration code. I also checked spam and all similar folders ... no code.

Can someone please help me with this issue ?

Thx.