When installing FreeBSD from an ftp/http it may complain that MANIFEST file is missing, to solve the problem this could be dona

Download the FreeBSD iso and unpack it into /tmp/iso:

$ tar xf FreeBSD-11.1-RELEASE-amd64-disc1.iso /tmp/iso

Start www in usr/freebsd-dist:

$ cd /tmp/iso/usr/freebsd-dist
$ www

This will expose the files via web so that they could be fetched

In the system where you want to install, fetch the MANIFEST file and save it in /usr/freebsd-dist/MANIFEST:

$ mkdir /usr/freebsd-dist
$ fetch x.x.x.x:800/MANIFEST -o /usr/freebsd-dist/MANIFEST

Hetzner

From the Hetzner robot go to your servers and then to the rescue and select FreeBSD as the operating system, after booting, edit /usr/sbin/bsdinstall and add:

export DISTRIBUTIONS="kernel.txz base.txz"
export BSDINSTALL_DISTDIR="/tmp/xyz"

Create dir /tmp/xyz and give a try using bsdinstall