Provisions an app gateway and a scale set

provision.sh

#!/bin/bash -e
set -e

location="westus2"
resource_group="dms-dev-10-rg"

ag_be_gw="dms-ag-backend-gw"
ag_be_pool="dms-ag-backend-pool"
ag_public_ip="dms-ag-public-ip"
ag_subnet="dms-app-gw-subnet"
ag="dms-app-gateway"
be_subnet="dms-backend-subnet"
ss_name="dms-scale-set"
vnet_name="dms-vnet"

# Create a resource group
echo "az group create"
az group create --name $resource_group --location $location

# Create network resources
echo "az network vnet create"
az network vnet create \
  --name $vnet_name \
  --resource-group $resource_group \
  --location $location \
  --address-prefix 10.0.0.0/16 \
  --subnet-name $ag_subnet \
  --subnet-prefix 10.0.1.0/24

echo "az network vnet subnet create"
az network vnet subnet create \
  --name $be_subnet \
  --resource-group $resource_group \
  --vnet-name $vnet_name \
  --address-prefix 10.0.2.0/24

echo "az network public-ip create"
az network public-ip create \
  --resource-group $resource_group \
  --name $ag_public_ip

# Create the application gateway
echo "az network application-gateway create"
az network application-gateway create \
  --name $ag \
  --location $location \
  --resource-group $resource_group \
  --vnet-name $vnet_name \
  --subnet $ag_subnet \
  --capacity 2 \
  --sku Standard_Medium \
  --http-settings-cookie-based-affinity Disabled \
  --frontend-port 80 \
  --http-settings-port 80 \
  --http-settings-protocol Http \
  --public-ip-address $ag_public_ip

# Install NGINX
echo "az vmss extension set"
  az vmss extension set \
  --publisher Microsoft.Azure.Extensions \
  --version 2.0 \
  --name CustomScript \
  --resource-group $resource_group \
  --vmss-name $ss_name \
  --settings '{ "fileUris": ["https://raw.githubusercontent.com/davidmu1/samplescripts/master/install_nginx.sh"], "commandToExecute": "./install_nginx.sh" }' 
 
# Get the IP address
echo "az network public-ip show"
az network public-ip show \
  --resource-group $resource_group \
  --name $ag_public_ip \
  --query [ipAddress] \
  --output tsv

This code, when running in my Azure account, dies during step "#######".

It emits the following error: