set service dhcpv6-server shared-network-name DHCPv6 subnet 2001:cafe:fefe::/48 address-range start 2001:cafe:fefe::100 stop '2001:cafe:fefe::1000'
set service dhcpv6-server shared-network-name PREFIX subnet 2001:cafe:fefe::/48 prefix-delegation start 2001:cafe:fefe:1111:: prefix-length '64'
set service dhcpv6-server shared-network-name PREFIX subnet 2001:cafe:fefe::/48 prefix-delegation start 2001:cafe:fefe:1111:: stop '2001:cafe:fefe:ffff::'

vyos@r4-epa# commit
[ service dhcpv6-server ]
VyOS had an issue completing a command.

Report time:      2021-10-19 22:13:39
Image version:    VyOS 1.3.0-epa2
Release train:    equuleus

Built by:         Sentrium S.L.
Built on:         Sun 17 Oct 2021 17:35 UTC
Build UUID:       2a282866-08cf-40fc-82a1-29ac261d3fb4
Build commit ID:  defac161082bc3-dirty

Architecture:     x86_64
Boot via:         installed image
System type:      KVM guest

Hardware vendor:  QEMU
Hardware model:   Standard PC (Q35 + ICH9, 2009)
Hardware S/N:     
Hardware UUID:    6f3ac57f-f80f-4b11-9abc-56bdc6f0e33d

Traceback (most recent call last):
  File "/usr/libexec/vyos/conf_mode/dhcpv6_server.py", line 183, in <module>
    verify(c)
  File "/usr/libexec/vyos/conf_mode/dhcpv6_server.py", line 131, in verify
    raise ConfigError('DHCPv6 subnets must be unique! Subnet {0} defined multiple times!'.format(subnet['network']))
TypeError: string indices must be integers