Either the service is down, or nordvpn has changed their api again.
The output of https://nordvpn.com/api/server is nothing.
The error message wasn't exactly helpful. If this happens often, it might make sense to check if the raw output is [] or {"message":"Not Found"} to catch some of these service down or API changes respectively?
Thanks for your work on it.
Possible alternatives are processing the outputs of:
https://api.nordvpn.com/v1/servers
https://api.nordvpn.com/server/stats
Hopefully it's just down.