db_parameter_group throws Error: first character of parameter group "name_prefix" must be a letter

[lgt]

Describe the Bug

As trying to spin up with minimal configuration a MySQL8 instance I keep getting the error above:

Error: first character of parameter group "name_prefix" must be a letter
with module.db.aws_db_parameter_group.default[0]
on .terraform/modules/db/main.tf line 126, in resource "aws_db_parameter_group" "default":
  name_prefix = "${module.this.id}${module.this.delimiter}"

Expected Behavior

the parameter group is creatd

Steps to Reproduce

data "aws_availability_zones" "available" {}

module "db" {
  source = "cloudposse/rds/aws"

  vpc_id               = data.terraform_remote_state.vpc.outputs.vpc_id
  engine_version       = "8.0"
  engine               = var.engine
  database_port        = var.database_port
  db_parameter_group   = "mysql8.0"
  parameter_group_name = ""
  instance_class       = var.instance_class
  availability_zone    = data.terraform_remote_state.vpc.outputs.azs[0]
}

Screenshots

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Environment

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Additional Context

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