Carsten Kurz:

Also, DCP-o-matic has a choice of creating SMPTE or Interop compliant DCPs AND KDMs - both need to fit either standard, and I suggest to go the 'old' Interop way, that is, create an encrypted Interop DCP, then create a KDM type 'Modified Transitional 1'

Tiny note there:

There are Interop and SMPTE KDMs. Interop KDM is deprecated. While you could find systems which expect Interop KDM if you look very hard you need to generate SMPTE KDM for both Interop and SMPTE DCPs.