with terraform version 13, I am getting error nvalid default value for variable in region params, how to fix that?

variables.tf

variable "region" {
  default = "us-central1"
}

variable "zone" {
  description = "override default zone specified in region_params"
  default     = ""
}

variable "region_params" {
  description = "Map of default zones for each region. Can be overridden using the `zone`."
  type        = map(string)

  default = {
    asia-east1 = {
      zone = "asia-east1-b"
    }
    asia-east2 = {
      zone = "asia-east2-b"
    }
    asia-northeast1 = {
      zone = "asia-northeast1-b"
    }
    asia-south1 = {
      zone = "asia-south1-b"
    }
    asia-southeast1 = {
      zone = "asia-southeast1-b"
    }
    australia-southeast1 = {
      zone = "australia-southeast1-b"
    }
    europe-north1 = {
      zone = "europe-north1-b"
    }
    europe-west1 = {
      zone = "europe-west1-b"
    }
    europe-west2 = {
      zone = "europe-west2-b"
    }
    europe-west3 = {
      zone = "europe-west3-b"
    }
    europe-west4 = {
      zone = "europe-west4-b"
    }
    northamerica-northeast1 = {
      zone = "northamerica-northeast1-b"
    }
    southamerica-east1 = {
      zone = "southamerica-east1-b"
    }
    us-central1 = {
      zone = "us-central1-b"
    }
    us-east1 = {
      zone = "us-east1-b"
    }
    us-east4 = {
      zone = "us-east4-b"
    }
    us-west1 = {
      zone = "us-west1-b"
    }
    us-west2 = {
      zone = "us-west2-b"
    }
  }
}

variable "network" {
}

variable "instance_tags" {
  default = []
}

variable "ip_cidr_range" {
  description = "Subnetwork range - required"
}

variable "environment" {
  description = "The build environment tier"
  default     = "dev"
}

output "nat-gateway-ip" {
  value = module.nat.external_ip
}

./terraform0.13 init -reconfigure

There are some problems with the configuration, described below.

The Terraform configuration must be valid before initialization so that
Terraform can determine which modules and providers need to be installed.
╷
│ Error: Invalid default value for variable
│
│   on variables.tf line 71, in variable "region_params":
│   71:   default = {
│   72:     asia-east1 = {
│   73:       zone = "asia-east1-b"
│   74:     }
│   75:     asia-east2 = {
│   76:       zone = "asia-east2-b"
│   77:     }
│   78:     asia-northeast1 = {
│   79:       zone = "asia-northeast1-b"
│   80:     }
│   81:     asia-south1 = {
│   82:       zone = "asia-south1-b"
│   83:     }
│   84:     asia-southeast1 = {
│   85:       zone = "asia-southeast1-b"
│   86:     }
│   87:     australia-southeast1 = {
│   88:       zone = "australia-southeast1-b"
│   89:     }
│   90:     europe-north1 = {
│   91:       zone = "europe-north1-b"
│   92:     }
│   93:     europe-west1 = {
│   94:       zone = "europe-west1-b"
│   95:     }
│   96:     europe-west2 = {
│   97:       zone = "europe-west2-b"
│   98:     }
│   99:     europe-west3 = {
│  100:       zone = "europe-west3-b"
│  101:     }
│  102:     europe-west4 = {
│  103:       zone = "europe-west4-b"
│  104:     }
│  105:     northamerica-northeast1 = {
│  106:       zone = "northamerica-northeast1-b"
│  107:     }
│  108:     southamerica-east1 = {
│  109:       zone = "southamerica-east1-b"
│  110:     }
│  111:     us-central1 = {
│  112:       zone = "us-central1-f"
│  113:     }
│  114:     us-east1 = {
│  115:       zone = "us-east1-b"
│  116:     }
│  117:     us-east4 = {
│  118:       zone = "us-east4-b"
│  119:     }
│  120:     us-west1 = {
│  121:       zone = "us-west1-b"
│  122:     }
│  123:     us-west2 = {
│  124:       zone = "us-west2-b"
│  125:     }
│  126:   }
│
│ This default value is not compatible with the variable's type constraint: element "asia-east2": string required.

Try setting it to us-central-1. You're formatting your regions wrong, you need a dash before the number. Additionally you don't need to specify a, b, or c since terraform gets the information from your subnet setting.