Their strict on who they accept as publishers now... quality of traffic is key and top geos.I see their publisher side never show option to register.
How much traffic does they need to approve your request?
As LordTyrion said, it depends on GEOs and volumes. I work with Kodio with a couple of my apps and I'm very satisfied. They do prefer to work with bigger players, but they are not neglecting smaller publishers either. Write them to their support email and ask for "Tjasa" - she's the most responsive one. She found me monetization options for my apps where I never thought I could monetize hahahI see their publisher side never show option to register.
How much traffic does they need to approve your request?