Ok, of course I found out how to do it just a few minutes later!
Set “Enable development mode” to true (Development mode allows the installation of Apps that are not from the Rocket.Chat’s Marketplace.). Go back to the top level “Apps” tab in Admin. You should now see a button labeled “Upload App”.
I am having the same issue. I have enabled development mode and i still receive error “Rocket.Chat Apps ➔ error Error getting the App information from the Marketplace: getaddrinfo ENOTFOUND marketplace.rocket.chat” when using upload app from file. Is there anything else i am missing?
Also where can i go to download apps for offline useage?
this seems to not work anymore in latest version? after uploading the zip file (poll.rc-app.zip) it says
"Invalid App Package. Could not find the classFile (PollApp.js) file.
this is rocketchat 3.10.5 and the latest downdload of the poll app