In PKGBUILD in package() the source file name for the installation of macfand.service is wrong.
package() {... install -Dm644 macfand.service "${pkgdir}/usr/lib/systemd/system/macfand.service" ... }
It must be called
package() { ... install -Dm644 macfand.service.gen "${pkgdir}/usr/lib/systemd/system/macfand.service" ... }
Otherwise package() fails with exit code 4