API V2 request for a Token on P1 meter fails with an 'invalid-json' error.

[jannegitje]

The problem

My P1 meter with firmware_version :6.0304 should support API V2.
I verified an open 443 https port via 'nmap '.

I tried to request a token according the example in the API V2 documentation on Authorization.

command:
curl https://<>/api/user --insecure -X POST -H "Content-Type: application/json" -H "X-Api-Version: 2" -d '{"name":"local/my_func"}'

Gave in first instance the error: {"error":"user:creation-not-enabled"}
Resending the command after pressing (within 30 seconds) the button on the P1 meter, it replied with the error {"error":"json:invalid-json"}

What could be the issue here that stops my Token Request?

Note that the API V1 is still operational.
command: curl http://<>/api returned with the device data.

I could use some help here.

Additional information

No response