Installing the Arduino Sam Boards core

Hello,

I am not able to install the Arduino SAM Boards core. When I click on Boards Manager, the list of cores to install does not appear. And only the error message appears, as in the image.
What do I need to do to get the Arduino SAM Boards core installed?

beatrizcnet’s picture:
7fb4f00d7845f37ff05f8e7711b65d3076b875d0.png

HTTP status code 407 is “Proxy Authentication Required”. You can configure the Arduino IDE’s proxy settings in the “Network” tab of File > Preferences.