"The following files conflict with new files to be generated" - Confused about the convention


I used phx.gen.json like so phx.gen.json X Y ys and it worked. Then I wanted to create a new one: phx.gen.json X Z zs and got this warning. When following this with Y now it shows an error " cannot expand struct X.X.X.Y".
When trying to use the pattern: X X xs and Y Y ys it was rejected either. Now, I am confused how I should go about it.

X is to me the app name
Y is a “module”
ys is plural to module