apt-get update error

# apt-get update

Err:1 https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64  InRelease

  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A4B469963BF863CC

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W: GPG error: https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64  InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A4B469963BF863CC

E: The repository 'https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64  InRelease' is no longer signed.

# apt-key del 7fa2af80

# apt-key adv --fetch-keys https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64/3bf863cc.pub

# apt-get update