Siedle HT511-01 Opener doesent work

My Intercom doesent work with the Opener. I connected it as recommend and as other door but it does pull the Voltage between I and c (the conntacts of the opener in the intercom) down to 12V (form 14.3V) so my door opens and is stuck. As long as The nuki opener is connected i cant open the door viva intercom or the app. Is the opener not working correctly? The door opener is an Multitronic 811.