child_process.exec() does not find calibre on deployed app

Weird error, when I run various ebook-anything locally it works fine, but when deployed I just get “NOT FOUND” on, for instance exec(“ebook-convert bla bla”)

I can run those commands in the local and remote terminal without problem. I have also tried with absolute path’s. Other commands like curl, ls and stuff works. But those are not what I need…

Any ideas?

I deployed it with MUPX, maybe that plays into this?