CI On Subdomain Configuration?

For me it's only a problem with the model: CodeIngniter doesn't find it... so why ?

when you search your problem with google you have some case like you: it's a problem of filenaming convention
in codeigniter 3 class file names now must be Ucfirst and everything else in lowercase link here

But it's possible it's another thing but verify before it was not a problem with the name of your model.