Before running gen.sh, make sure fastd (and tunneldigger for l2tp domains) are installed. You can get tunneldigger from this repository. Check out the master branch, install the following build dependencies (ubuntu/debian package names):
$ sudo apt install -y build-essential cmake pkg-config libnl-3-dev
$ git clone https://github.com/wlanslovenija/tunneldigger
$ cd tunneldigger
$ mkdir build
$ cd build
$ cmake ../client
$ make
$ sudo make install