While adding default gateway, I am facing below error
address: fda8:06c3:ce53:a890:0000:0000:0000:0001 prefixlen 64
gateway: fda8:06c3:ce53:a890:0000:0000:0000:0005

# route -v add -inet6 fda8:06c3:ce53:a890:0000:0000:0000:0005/64%tiw_sta0 

so_dst: inet6 fda8:6c3:ce53:a890::5; so_mask: inet6 ffff:ffff:ffff:ffff::; 
RTM_ADD: Add Route: len 120, pid 0, seq 1, errno 0, flags: <UP,GATEWAY,STATIC>
locks:  inits: 
sockaddrs: <DST,NETMASK>
 fda8:6c3:ce53:a890::5 ffff:ffff:ffff:ffff::
route: writing to routing socket: Invalid argument
add net fda8:06c3:ce53:a890:0000:0000:0000:0005/64%tiw_sta0: Invalid argument

Could you please help in resolving this issue??

tiw_sta0: flags=8c43<UP,BROADCAST,RUNNING,OACTIVE,SIMPLEX,MULTICAST> mtu 1504
        address: 34:b1:f7:8c:5e:a1
        media: IEEE802.11 autoselect
        status: no network
        inet6 fe80::cab3:73ff:fe0f:335d%tiw_sta0 prefixlen 64 scopeid 0x4
        inet6 fda8:6c3:ce53:a890::1 prefixlen 64
			
Internet6:
Destination                             Gateway    Flags    Refs      Use    Mtu  Interface
::1                                           ::1                  UH          0        0  33192  lo0
fda8:6c3:ce53:a890::/64       link#4             UC          0        0      -      tiw_sta0
fe80::%lo0/64                        fe80::1%lo0    U           0        0      -      lo0
fe80::%en0/64                      link#2             UC          0        0      -       en0
fe80::%tiw_sta0/64              link#4             UC          0        0      -       tiw_sta0
ff01:1::/32                             ::1                  UC          0        0      -       lo0
ff01:2::/32                             link#2             UC          0        0      -       en0
ff01:4::/32                             link#4             UC          0        0      -       tiw_sta0
ff02::%lo0/32                        ::1                  UC          0        0      -       lo0
ff02::%en0/32                       link#2             UC          0        0      -       en0
ff02::%tiw_sta0/32               link#4             UC          0        0      -       tiw_sta0