create-auto-scaling-group with MixedInstancesPolicy

i am following this guide https://docs.aws.amazon.com/autoscaling/ec2/userguide/asg-purchase-options.html

to create auto-scale group with different type of ec2 types , (fleet) but getting error in return.
is this not active yet in region=eu-west-1 ?

even using there example return same error:
/usr/local/aws/bin/aws autosc
aling create-auto-scaling-group --auto-scaling-group-name tmp-eli --cli-input-js
on '{"AutoScalingGroupName":"tmp-eli","MixedInstancesPolicy":{"LaunchTemplate":{
"LaunchTemplateSpecification":{"LaunchTemplateName":"lt-10349","Version":"v1"},"
Overrides":[{"InstanceType":"c4.2xlarge"},{"InstanceType":"c5.2xlarge"},{"Instan
ceType":"c5d.2xlarge"}]},"InstancesDistribution":{"OnDemandBaseCapacity":0,"OnDe
mandPercentageAboveBaseCapacity":50,"SpotInstancePools":2}},"MinSize":2,"MaxSize
":100,"DesiredCapacity":4,"VPCZoneIdentifier":"subnet-ae6a6ed8,subnet-aa2c6ef2,s
ubnet-07c8ce63","Tags":[]}' --output json

Parameter validation failed:
Unknown parameter in input: "MixedInstancesPolicy", must be one of: AutoScalingGroupName, LaunchConfigurationName, LaunchTemplate, InstanceId, MinSize, MaxSize, DesiredCapacity, DefaultCooldown, AvailabilityZones, LoadBalancerNames, TargetGroupARNs, HealthCheckType, HealthCheckGracePeriod, PlacementGroup, VPCZoneIdentifier, TerminationPolicies, NewInstancesProtectedFromScaleIn, LifecycleHookSpecificationList, Tags

any idea?

eli