Please check that the PPA name or format is correct. Issue

configure your  /etc/apt/apt.config file as follows: etc/apt/apt.config

Acquire::http::proxy "http://<username>:<password>@<proxy address>:<port>/";

 export your proxy environment variables using

export http_proxy=http://username:password@host:port/
export https_proxy=https://username:password@host:port/

and then tell sudo to use them using:

 sudo -E add-apt-repository ppa:webupd8team/y-ppa-manager