Shelly Pro 3EM and 4th clamp/CT on N/PEN

I have Shelly Pro 3EM 120A (gen2)

• Device name: Shelly Pro 3EM
• Device model: SPEM-003CEBEU

see knowledge-base/shelly-pro-3em.

I bought an additional split-core current transformer, Shelly CT 120A,

• SHELLY SP3D-1121
• EAN/GTIN: 3800235266410

I plug all 4 CTs and all 4 wires.

I can access the device

• locally via its IPv4
• via Home Assistant and its Shelly integration
• via Shelly Cloud (app and page)

I see current on phases A/B/C, but I do not see any value of N/PEN.

What is wrong there?

Should I activate some additional settings in the configuration to make N/PEN visible? And where?

Does N/PEN measuring work for anybody?

When I choose local IP of Shelly Pro 3EM

export SHELLY_IPV4='<MY_LOCAL_IP>'

then I see the status via command

curl --silent --request POST --data '{"id":1,"method":"Shelly.GetStatus"}' http://${SHELLY_IPV4}/rpc | jq '.result.sys'

Similarly, I can see the configuration via the command

curl --silent --request POST  --data '{"id":1, "method":"EM.GetConfig", "params":{"id":0}}'  http://${SHELLY_IPV4}/rpc | jq '.result'

And when I want to see current values, then I use the command

curl --silent --request POST --data '{"id":1,"method":"Shelly.GetStatus"}'  http://${SHELLY_IPV4}/rpc | jq '.result."em:0"'

where I see a non-zero value for a_current` but null value for n_current.

Nope, I didn't run any calibration.

I'm not aware of it. I'm going to look for howto