Sound issue Urmet 1750/2 ring Intercom

Installed our new Ring Intercom tonight. See photo, orange is on the side at LINE and the yellow wire at IN. If we do this the other way round then it doesn't work, so this seems so right. When we ring at the front door we get a notification on our mobiles. Only when we pick up do we hear a very loud beep, both outside at the front door and on our mobiles. We can't understand anything this way. We can, however, open the door. That works.