I tried to follow this guide to do it but the pi disables them because it cannot verify the keys. Does someone have a way to do this? I'm on raspberry pi 3.
precicely this is the error i got
Err:1 http://ftp.us.debian.org/debian sid InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
Reading package lists... Done
W: GPG error: http://ftp.us.debian.org/debian sid InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
E: The repository 'http://ftp.us.debian.org/debian sid InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.