I was reading through the swagger calls, but couldn't figure out where I could get this info.
This thread was automatically locked due to age.
Hola Mauro and welcome to the UTM Community!
Not sure about how to do that with the Rest API, but you can find the information about the leases at:
/var/sec/chroot-dhcps/var/state/dhcp/dhcpd.leases
Cheers - Bob