AUR or Arch Linux User Repository is a huge collection of PKGBUILDS that will install thousands of applications on your system. It will install on anything Arch Linux based.
Sometimes packages break.
The reason are too diverse to go into.
In this particular case the URL does no longer exists. Ubuntu has deleted or renamed the package and you get a 404 response.
The installation of the package halts.
Solution
Help yourself and others by creating an account on the AUR and flag the package out-of-date.
The maintainer will get a mail that the pkgbuild needs to be updated and wait …