Soundiiz is available for Beatport LINK and Beatsource LINK offers. However, even if a track is available in the Beatport or Beatsource catalog, that doesn't mean this same track is available in the LINK offer.
The LINK offer is a streaming offer different from the catalog on Beatport or Beatsource. Music owners could not have allowed their songs' LINK (streaming) usage.
That's why some songs cannot be matched by Soundiiz while available on Beatport or Beatsource.