Spotify repository missing public key

[Mince]

I am running Spotify on my Linux Mint Desktop (21.3 Cinnamon).  I get this error message, which was too long to serve as a title (I was able to edit the question title):

GPG error: http://repository.spotify.com stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6224F9941A8AA6D1The repository 'http://repository.spotify.com stable InRelease' is not signed.

Installed Spotify (system package) on Linux Mint 21.3. The system complains that the Spotify repository is unsigned.
What command do I need to run in the Terminal to correct the issue?

Spotify is working just fine, but I suspect there will come a time to upgrade the package.

I discovered how to edit after I posted the information in a reply.

Thank you.

[Mince]

I posted the error code here after I found it too long for the title above, but then I found how to edit my original post, making this one moot.

[Mince · Accepted solution]

I have a solution to fix my issue.  Spotify for Linux has a code that I can run to configure the repository:

curl -sS https://download.spotify.com/debian/pubkey_6224F9941A8AA6D1.gpg | sudo gpg --dearmor --yes -o /etc/apt/trusted.gpg.d/spotify.gpg

There were two lines, but I had to enter them one at a time, because the sudo took the second line in my Terminal as a very long and invalid password.  Enter your sudo password, then enter the second line:

echo "deb http://repository.spotify.com stable non-free" | sudo tee /etc/apt/sources.list.d/spotify.list

Let all of that run.  Then, you can install the Spotify client:

sudo apt-get update && sudo apt-get install spotify-client

I ended up with a 2024 version of Spotify with more features than I had to begin with.

The site also offers a snap version.  However, I don't use the snap store.

[brezanac]

Mint also provides an easy option to fix this issue in the Maintenance section of their Software Sources app.

By simply clicking on the Add missing keys button all the missing keys, including the one for Spotify, will be fetched and installed.

[theLiuk23]

The fix for me was to remove all the previous authentication keys (in Software Sources as mentioned by @brezanac) and then click "add missing keys".

[shimrah]

The "marked as solution" terminal commands did not fix my problem, but Adding missing keys via the Software Sources did. Thanks, brezanac!