If you know the IP-address of your Kobo (for example 192.168.1.123)
Add this line to your .htaccess file
Code:
allow from 192.168.1.123
If you want all your divices to access COPS on your Synology without authentication add this line to your .htaccess file:
Code:
allow from 192.168.1.0/24
This should solve (at least one) of your problems.