Nix sample flak app: nodename nor servname provided, or not known

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1

I tried the sample application but all I get when I run it from inside the shell is:
nodename nor servname provided, or not known

I have tried many things since to make it work. I installed a virtual environment outside the shell, pip installed flask and

(env) ➜  learn1 export FLASK_APP=myapp
(env) ➜  learn1 flask run
 * Serving Flask app 'myapp' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000 (Press CTRL+C to quit)

it works, however, with the code as supplied from the tutorial sample:

[nix-shell:~/Documents/code/nix/learn1]$ myapp
 * Serving Flask app 'myapp' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
nodename nor servname provided, or not known

Currently I am out of ideas. Running on Monteray M1.

I’d like to use Nix=os instead of docker as the main way to containers things but if it can’t even run a simple sample then I don’t know!