Please whitelist the following IP addresses:
34.227.212.80
3.83.70.104
65.108.217.1
95.217.244.243
3.66.2.188
You could trying the following commands on your server to whitelist SimpleBackups by adding it's IP addresses to the firewall. In the example below, we are whitelisting post 22 on a Linux machine.
sudo ufw allow from 34.227.212.80 to any port 22
sudo ufw allow from 65.108.217.1 to any port 22
sudo ufw allow from 95.217.244.243 to any port 22
sudo ufw allow from 3.83.70.104 to any port 22
sudo ufw allow from 3.66.2.188 to any port 22
To whitelist an IP on your database for example, you may check these guides if they are similar to your case: