CUDNN Installing error

I am following the NVIDIA CUDNN documentation https://docs.nvidia.com/deeplearning/cudnn/install-guide/index.html#package-manager-ubuntu-install to install cudnn on my linux machine (Ubuntu20.04). However when i go to run →

wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/cuda-ubuntu2004.pin 

sudo mv cuda-ubuntu2004.pin /etc/apt/preferences.d/cuda-repository-pin-600
sudo apt-key adv --fetch-keys https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/7fa2af80.pub
sudo add-apt-repository "deb https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/ /"
sudo apt-get update 

the following is outputted:

Get:1 http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64  InRelease [1,581 B]
Hit:2 http://deb.anydesk.com all InRelease                                     
Hit:3 http://security.ubuntu.com/ubuntu focal-security InRelease               
Hit:4 http://mt.archive.ubuntu.com/ubuntu focal InRelease                      
Err:1 http://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
Hit:5 http://mt.archive.ubuntu.com/ubuntu focal-updates InRelease   
Hit:6 http://mt.archive.ubuntu.com/ubuntu focal-backports InRelease 
Ign:7 http://developer.download.nvidia.com/compute/machine-learning/repos/ubuntu1804/x86_64  InRelease
Hit:8 http://developer.download.nvidia.com/compute/machine-learning/repos/ubuntu1804/x86_64  Release
Ign:9 https://developer.download.nvidia.com/compute/cuda/repos//x86_64  InRelease
Get:10 https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease [1,581 B]
Err:10 https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A4B469963BF863CC
Err:12 https://developer.download.nvidia.com/compute/cuda/repos//x86_64  Release
  404  Not Found [IP: 152.199.20.126 443]
Reading package lists... Done
W: GPG error: http://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 'http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64  InRelease' is no longer 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.
W: GPG error: https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/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/ubuntu2004/x86_64  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.
E: The repository 'https://developer.download.nvidia.com/compute/cuda/repos//x86_64  Release' does not have a Release file.
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.

Could anyone help with this?
Thanks.

Hi,

Could you please try the following.
https://chrisjean.com/fix-apt-get-update-the-following-signatures-couldnt-be-verified-because-the-public-key-is-not-available/

Thank you.