I just received an invite from a friend to join his competition. However, I can't, because I have no free slots. I am only playing on the first slot though. I have been a couple of years on OSM, but only played one competition after the apparent update of the game. I am not familiar with the unlocking time yet, but I think I have waited long enough for at least the 2nd slot to unlock. So, I think something is wrong (see picture).
Can anyone enlighten me?