I’m not sure what the fuss is about? Have I missed something? I have never tried to pre-enter my API for LO flights. When you start the online checkin process it will ask for your passport info and it works just fine. Just wait for that.
It’s entirely operated and managed by Amadeus and works just fine...? Even the boarding pass emails come from an Amadeus address.
Entering API at OLCI is how I, and probably ever other LO OLCI pax does it.