Nuki Opener & Siedle HT611-01 only connected to c and I

Hi Forum,

my Siedle HT611-01 seems to be connected other way than assumed by Nuki Opener.
Only 2 Wire from the house are connected to c (see green wire) and I (see brown wire).
Can anybody give me a hint to understand the concept?

See also the fotos I took:

Thanks … Jörg