Re: Bought seed slot but not enough seeds

@Kalist42  I may have a workaround for you.  

Could you try entering the store and select the Adventure section (like image below). In this section you should find the Daily Gift and seeds which you can exchange with coins and gems.  Hopefully, once you have collected enough seeds to unlock one more plant, the game would allow you start playing the levels.  Please let us know if this works for you.