If you want to VPN into your network using the Meraki Cloud Controller the Client VPN Instructions indicate that you may be out of luck when trying to use xl2tp.
It turns out that if you setup the IPSEC phase1 and phase2 algorithms then it’ll work.
It took some googling to bring it all around but combined with the Project network-manager-l2tp Github issue 34 of “IPSec options hard coded” and the Ubuntu question “L2tp IPSEC PSK VPN client on (x)ubuntu 16.04“, I found that setting IPSEC Phase1 Algorithms to 3des-sha1-modp1024 and Phase2 Algorithms to 3des-sha1 works.
Now I can connect to the VPN no problem. On Arch Linux!