Hi Vsevolod,
It looks like you don't have any thresholds set within your match configuration, this is what causing the error here. Once you set one you shouldn't see this error. You can read about how to set thresholds here. If you have any further questions just let me know.
Thanks,
Liam
Vsevolod Miroshnikov
{ "@class": ".MatchmakingRequest", "matchShortCode": "1", "skill": 0 }
{ "@class": ".MatchmakingResponse", "error": { "matchShortCode": "NOT_FOUND" } }