Based on the original post https://doc.pfsense.org/index.php/Remote_Config_Backup

As of pfSense 2.3, the method to perform a remote config backup has changed. The article above details the multiple requests needed to perform a remote config backup from a terminal however it leaves a bit out and doesn’t give an easy way to backup multiple sites or routers.

I’ve created a bash script which can be used as a tool to download multiple sites and fix a few issues with the original article.
To use, copy the code and save as a shell file (such as backupscript.sh) then chmod +x the script file.
Run the script like this:

./backupscript.sh 192.168.1.1 443 admin ‘pAsSwD’ ‘myEnCKeY’ ~/configbackups

Always make sure to check your config file after you run this script. If the script fails to login, it will still generate a config file but the contents will not be what you expect.