ERROR: ssl certificate doesn't exist: /home/rsvay/snap/barrier-kvm/2/.local/share/barrier/SSL/Barrier.pem

Copy the path to SSL directory which you can find in your error. "ERROR: ssl certificate doesn't exist: /home/rsvay/snap/barrier-kvm/2/.local/share/barrier/SSL/Barrier.pem "
In this case : "/home/rsvay/snap/barrier-kvm/2/.local/share/barrier/SSL/"

Then run the following commands:

cd  "path to your SSL"
mkdir -p Fingerprints
openssl req -x509 -nodes -days 365 -subj /CN=barrier -newkey rsa:4096 -keyout Barrier.pem -out Barrier.pem
openssl x509 -fingerprint -sha1 -noout -in Barrier.pem > Fingerprints/Local.txt
sed -e "s/.*=//" -i Fingerprints/Local.txt

You can disable the SSL Fingerprint from the barrier setting in both server and client. Then it will work smoothly.

Rsvay's solution worked for me after I corrected the file name. capitalize the B: change 'barrier.pem' to 'Barrier.pem'

$ mv ~/.local/share/barrier/SSL/barrier.pem ~/.local/share/barrier/SSL/Barrier.pem

It worked for me in Ubuntu 20.04. However the barrier.pem file generated after running the code is case sensitive, I had to change to Barrier.pem and it runs perfectly.

https://github.com/debauchee/barrier/discussions/1682

The paths may not align but if you follow the steps, you'll get it working. Win 10 & Ubuntu 20.04. Had to go to ~/snap/barrier/<3digit#>/.local/share/barrier/SSL and created the Fingerprints folder.

Stay in this directory to run the script that is mentioned.

(You have to create a text file Local.txt in the Fingerprints directory but run the script from SSL).