When importing DHCP ranges, you need to specify the ID of the dhcp_host. It won't inherit or detect a host set at the parent subnet level.

When dealing with importing data, you need to set a name and key. The key is “custom_list/NAME_OF_LIST” in base64 format where NAME_OF_LIST is the value of “name” under “key”. That is to say, take the name (e.g. NAME_OF_LIST) and convert to base64.

openssl base64 -in unencoded.txt -out encoded.txt