ipv6AddressCount
The number of IPv6 addresses to assign to a network interface. Amazon EC2 automatically selects the IPv6 addresses from the subnet range.
You can't specify a count of IPv6 addresses using this parameter if you've specified one of the following: specific IPv6 addresses, specific IPv6 prefixes, or a count of IPv6 prefixes.
If your subnet has the AssignIpv6AddressOnCreation
attribute set, you can override that setting by specifying 0 as the IPv6 address count.