I solved it .
It was mix of small little problems that together hindered the correct answer:
- changed in golang webserver HOST = 127.0.0.1
- capitalized the first letter of each element of the Puser struct in order to make it visible to json decoder
- used correctly the curl command:

curl -d'{"first_name":"pinco", "last_name":"pallo", "company_name":"Company","email":"pinco.pallo@company.com","tel":"111111111"}' -H "Content-Type: application/json" 127.0.0.1:2000/puser/add
[{"First_name":"pinco","Last_name":"pallo","Country":"","Company_name":"Company","Email":"pinco.pallo@company.com","Tel":"111111111"}]