Apt update reporting signature cannot be verified

Hi,

whenver I am running apt update I am seeing thsi error:

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://apt.radxa.com/bionic bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B99C4BEFEC47E96E
W: Failed to fetch http://apt.radxa.com/bionic/dists/bionic/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B99C4BEFEC47E96E
W: Some index files failed to download. They have been ignored, or old ones used instead.

Does anyone know how this can be fixed ?

Hello. Try adding the public key to the apt keyring.

wget -O - apt.radxa.com/bionic/public.key | sudo apt-key add -