I have tried following these instructions for updating to DSM 7.1 from 7.0.1 using Proxmox.
Unfortunately after hours of attempts this morning I wasn't able to get it working.
So I decided to wipe Proxmox and go Bare Metal with DSM 7.1.
Then following these instructions worked perfectly without any headaches.
Since DSM is installed on the hard disk I did not lose any data converting from Proxmox to Baremetal.
The only thing that has changed is having to leave a USB stick plugged in at all times.
Thanks Peter Suh for the amazing instructions and on top of that for providing the shell script above!