Unable to add IPV6 Route in GCP

we have a requirement where we need to create a floating Ip and it should be moved across the GCP Compute Instances. In this case we need to add the route under the route table of the VPC(asia-south1) with the floating IP entry(2600:1f18:1802:4b04:b8f7:9c39:4458:1a05).

Note: IPV6 is supported for the region that we have used.

Please refer to below error when we tried adding the route: Error:

Creating route "allow-ipv6-vpc-route" failed. Error: Invalid value for field 'resource.destRange': '2600:1f18:1802:4b04:b8f7:9c39:4458:1a05'. IPv6 destination range can only be specified for routes with Internet gateway.

Note:Any route we are adding is reporting similar issues

GCP-CONSOLE-ERROR