Unable to create a dual stack VM in Google Cloud - IPv6 access config is not supported for this network interface

Question

My objective is to set up internal protocol forwarding using IPv6.

I am running the following command and getting stuck at step 4 - Create a dual stack VM.

The process that I have followed is as follows:

1. Create a custom mode VPC:

gcloud compute networks create lb-network \
  --subnet-mode=custom
  --enable-ula-internal-ipv6

2. Create a dual stack subnet:

gcloud compute networks subnets create lb-subnet \
  --stack-type=IPV4_IPv6 \
  --ipv6-access-type=INTERNAL \
  --network=lb-network \
  --range=10.1.2.0/24 \
  --region=asia-east1

3. Create a firewall rule to allow SSH connectivity to VMs:

gcloud compute firewall-rules create firewall-allow-ssh \
--network=lb-network \
--target-tags=allow-ssh \
--allow=tcp:80 \
--source-ranges=0::0/0

4. Create a dual stack VM:

gcloud compute instances create vm-1 \
--zone=asia-east1-a \
--ipv6-network-tier=PREMIUM \
--subnet=lb-subnet \
--stack-type=IPV4_IPV6 \
--image-family=debian-10 \
--image-project=debian-cloud \
--tags=allow-ssh \
--subnet=lb-subnet \
--metadata=startup-script='#! /bin/bash
sudo apt-get update
sudo apt-get install apache2 -y
sudo a2ensite default-ssl
sudo a2enmod ssl
vm_hostname="$(curl -H "Metadata-Flavor:Google" \
http://169.254.169.254/computeMetadata/v1/instance/name)"
echo "Page served from: $vm_hostname" | \
tee /var/www/html/index.html
sudo systemctl restart apache2'

At this step, i get the following error:

ERROR: (gcloud.compute.instances.create) Could not fetch resource:
 - Invalid value for field 'resource.networkInterfaces[0].ipv6AccessConfigs': ''. IPv6 access config is not supported for this network interface.

It seemed to have worked fine when I created external protocol forwarding using IPv6.

Can you please guide me what I could be missing here.