gRPC as a protocol version for ALB target_group

Terraform Providers AWS
1 
    aws = {
      source  = "hashicorp/aws"
      version = "3.57.0"
    }

AWS have added support for gRPC workloads with end to end HTTP/2 to the Application Load Balancer.

From the docs it seems it is possible to pass gRPC as a protocol_version attribute of the aws_lb_target group and HTTP as a protocol, but this didn’t work when deploying and I got HTTP1 as a protocol version instead of GRPC.

any idea what went wrong or what should I improve in the script or on aws side?

this is how my terragrunt.hcl file looks like:

inputs = {
  name              = local.name
  environment       = local.environment
  target_group_name = local.name

  ecs_use_fargate = true
  ecs_vpc_id      = dependency.vpc.outputs.vpc_id
  ecs_subnet_ids  = dependency.vpc.outputs.app_subnet_ids
  ecs_cluster_arn = dependency.cluster.outputs.ecs_cluster_arn

  ecr_create = true

  associate_alb      = true
  container_port     = local.app_port
  alb_security_group = dependency.alb.outputs.alb_security_group_id
  lb_listener_arn    = dependency.alb.outputs.alb_http_listener_arn
  protocol           = "HTTP"
  protocol_version   = "GRPC"
  matcher            = "12"
  lb_target_ports    = [local.app_port]
  health_check_path  = local.health_check_path