Clone Windows with Single NIC, Invalid Subnet Mask with IPv6

Hi guys,

I'm trying to create a new vm based on the workflow Clone Windows with Single Nic. All works good with IPv4, but when I try to use IPv6 at the new vm I'm getting the error at vCenter that the subnet mask is invalid. Is there something that I need to set to use IPv6? What is the correct format to set the subnet?

thanks!