Apparently you can't use this set in XY if you are using the application. For some reason you can only use this set when playing Pokémon Online on a webbrowser. Thats really weird since that set was also useable back in XY.
The webclient lacks moveset checks right now and relies on the server as far as I know. However I did verify that this is happening on my own computer (which definitely gives Scolipede Toxic Spikes as an egg move in subgen 0). I have no idea what's causing that since the database seems to show that it has the egg move.
Fixed. Endeavor is a gen 5 move and the move checker got confused by Scolipede's hidden ability changing in gen 6.