If Nuxeo can't access the web, when I go to the admin center, I can't update it with my Nuxeo Studio project. Can I download the plugin of my Nuxeo Studio project somehow and install it in my Nuxeo?
You can download your plugin from Nuxeo Studio by clicking on "Download"./> Put the downloaded jar in $NUXEO_HOME/nxserver/plugins/ directory of your Nuxeo and restart the server.
Check you don't have other versions of your plugin installed in $NUXEO_HOME/nxserver/plugins/ or $NUXEO_HOME/nxserver/bundles/.