The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 77B79B3FFAF7EF65

whenever i run sudo apt update i get this error:

Hit:1 http://mirrors.digitalocean.com/ubuntu jammy InRelease
Hit:2 http://mirrors.digitalocean.com/ubuntu jammy-updates InRelease                                                                                                               
Hit:3 http://mirrors.digitalocean.com/ubuntu jammy-backports InRelease                                                                                                             
Hit:4 https://repos-droplet.digitalocean.com/apt/droplet-agent main InRelease                                                                                                      
Hit:5 http://security.ubuntu.com/ubuntu jammy-security InRelease                                
Get:6 https://repos.insights.digitalocean.com/apt/do-agent main InRelease [5518 B]              
Err:6 https://repos.insights.digitalocean.com/apt/do-agent main InRelease 
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 77B79B3FFAF7EF65
Fetched 5518 B in 1s (4960 B/s)
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repos.insights.digitalocean.com/apt/do-agent main InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 77B79B3FFAF7EF65
W: Failed to fetch https://repos.insights.digitalocean.com/apt/do-agent/dists/main/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 77B79B3FFAF7EF65
W: Some index files failed to download. They have been ignored, or old ones used instead.

There’s some digital ocean posts about this but none of the solutions work anymore

I found the solution Removing digital ocean agents from here /etc/apt/sources.list.d by going to the directory with

cd /etc/apt/sources.list.d

then ls to list the files then remove them both by using

rm -rf (name of file)

for all the agents and then running

sudo apt purge droplet-agent*

and

wget -qO- https://repos-droplet.digitalocean.com/install.sh | sudo bash