Portainer behind a proxy

My organization uses a proxy to access the Internet. When i open the “extensions” tab, i get error "Failure
Get https://portainer-io-assets.sfo2.digitaloceanspaces.com/extensions-1.22.0.json: net / http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) "
I tried to create a container with the key -e HTTP_PROXY = my.proxy.domain: 7777 - but when container start an error occurred “unknown short flag ‘-e’” .

Have you tried --env instead of -e ? Can you provide your full command ?