Zabbix x509: certificate signed by unknown authority

Hi,
i downloaded Grafana 7 and plugin Zabbix 4.0.0.
I add into grafana.ini:
[plugins]
allow_loading_unsigned_plugins = alexanderzobnin-zabbix-datasource
app_tls_skip_verify_insecure = true

but i have this error:
x509: certificate signed by unknown authority

Could you help me?
If i use Grafana 6.5.2 and PluginZabbix 3.10.5 is ok.

Thanks
FRancesco