You haven't posted what browser you're using or the version which is what the error states.

The browser doesn't matter. The VPN probably has settings to block scripts.

At that point a script should automatically test your browser to weed out bots.

Check your VPN settings.

The NordVPN website FAQs say they're having issues with CAPTCHA and are working on it. (Not sure how long ago it was updated).

I just couldn't get it to work with Chrome for Android. I've not tried a desktop browser or Firefox Android.

FWIW I think that's a quite generic (and misleading) Cloudflare error message. 

I used to get it on a bunch of websites when I was globally blocking service workers and didn't have cloudflare.com in my whitelist, so the above about scripts being blocked is probably accurate.

From a security perspective also I strongly recommend you don't use public VPN services: https://overengineer.dev/blog/2019/04/08/very-precarious-narrative/

If you need a VPN to get past restrictions then perhaps look into setting up a VM somewhere to run a Tailscale exit node on (this gets past most blocks).

This advise comes from purely a security perspective. I would not at all trust any provider like NordVPN etc at all. They're often abused for malicious purposes so trust is also very very low for public VPN IP addresses.