I once ran into this exact problem, OC by default disables localhost specifically with this default config
blacklist=[
"127.0.0.0/8",
"10.0.0.0/8",
"192.168.0.0/16",
"172.16.0.0/12"
]
the config supports domain names op addresses in string format and even CIDR notation for easy address ranges.
the reason for this is apparently to prevent user from hosting their game locally and accidentally letting other people access their computers through OC.
If you arent in multiplayer its probably safe to remove this from the config and othherwise you'll have to ge