"The error message denotes that there is an error somewhere in SSL/TLS handshake. In short, the cURL error code 35 denotes an SSL connection error. The error can be due to an outdated cURL package, connection errors or else a version mismatch between the PHP cURL and SSL protocol of the end server"
Make sure your firewall does't block our IPs
There might be different reasons for this error.
First thing I'll ask you to check is to make sure your server has doesn't block our IP adresses:
You could try the following commands on your server to whitelist SimpleBackups by adding it's IP addresses to the firewall.
sudo ufw allow from 184.108.40.206 to any port 22
sudo ufw allow from 220.127.116.11 to any port 22
sudo ufw allow from 18.104.22.168 to any port 22
Make sure your cURL version is up-to-date
Check your OS update method for upgrading cURL package.