Kibana plugin certificate error

[111505 (taewoo kim)]

Hi
I need Kibana css plugin.
So I wrote the command below.

./kibana-plugin install file:///usr/local/ELK_7.9.2/kibana-7.9.2-linux-x86_64/kibana-dashboard-custom-css-master.zip
However, I get an authentication error as below.

Picked up proxy http://[MY PROXY IP] from environment variable.
Error: Client request error: unable to verify the first certificate
Plugin installation was unsuccessful due to error "Client request error: unable to verify the first certificate"

Http has no problem with the proxy, why am I getting a proxy error? Does Kibana-plugin use a different communication method?

[Mikhail_Shustov]

@111505

Picked up proxy http://[MY PROXY IP] from environment variable.

It means the certificate chain is incomplete. Are you sure Kibana doesn't try to use https protocol?
Do you have NODE_EXTRA_CA_CERTS env variable set?