What is the best way to import networks from your IPAM server into DNA-C? Can it only be done manually or is there a way via APIs because I can't find a direct API call for it?
You can import the IP Pools from the IPAM server using the Cisco DNA Center Admin UI. There is an "Import from IPAM Server" action in the Design - Network Settings - IP address Pools section.
Note: There is a CAVEAT. The IP address Pool(s) on the IPAM server MUST be empty and not in use. No configuration or client use. If the IP address pool(s) do not meet this restrictions, you can not import them.
This is a known limitation at this time.