Ubuntu – The template parameter is not valid. The parameter value must be null

I’m a beginner on Azure DevOps and I’m trying to create a CI pipeline for an simple ARM Template. So I have this file (test_template.json):

{
    "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "storageAccounts_dqed01dls_name": {
            "defaultValue": "dqed01als",
            "type": "String"
        },
        "virtualNetworks_dpm01_d_vnet_externalid": {
            "defaultValue": "/subscriptions/xxx1234/resourceGroups/dpm01-vnets-d-rg/providers/Microsoft.Network/virtualNetworks/dpm01-d-vnet",
            "type": "String"
        },
        "Environment": {
            "value": "Acc",
            "type": "string"
        }
    },
    "variables": {},
    "resources": [
        {
            "type": "Microsoft.Storage/storageAccounts",
            "apiVersion": "2021-09-01",
            "name": "[parameters('storageAccounts_dqed01dls_name')]",
            "location": "westeurope",
            "tags": {
                "CBSPProduct": "Storage 4.0.1",
                "AppName": "DQEM",
                "Billing code": "XX000",
                "Business Application CI": "XX00546",
                "CIA": "001",
                "ContactMail": "[email protected]",
                "ContactPhone": "+390000000",
                "Environment": "[parameters('Environment').value]",
                "Owner": "[email protected]",
                "Provider": "PTV_Azure"
                
(...)

And also this parameter file (test_parameters.json), which I have no idea why it exists because this parameters are also defined in the ARM template above

{
    "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "storageAccounts_dqed01dls_name": {
            "value": "dqed01dls"
        },
        "virtualNetworks_dpm01_d_vnet_externalid": {
            "value": "/subscriptions/xxx1234/resourceGroups/dpm01-vnets-d-rg/providers/Microsoft.Network/virtualNetworks/"
        },
        "Environment": {
            "value": "Acc"
        }
    }
}

Then, I run this YAML pipeline:

# Starter pipeline
# Start with a minimal pipeline that you can customize to build and deploy your code.
# Add steps that build, run tests, deploy, and more:
# https://aka.ms/yaml

trigger:
- "*"

parameters:
- name: Environment
  displayName: Environment
  type: string
  default: ubuntu-latest
  values:
  - Dev
  - Acc
  - Prod

stages:
  - stage: test
    jobs:
      - job: 'validateandtest'
        pool:
          vmimage: windows-latest
        steps:
        - task: AzureResourceManagerTemplateDeployment@3
          inputs:
            deploymentScope: 'Resource Group'
            azureResourceManagerConnection: 'dpm01-devops-a-rg'
            subscriptionId: 'xxx1234'
            action: 'Create Or Update Resource Group'
            resourceGroupName: 'dpm01-devops-a-rg'
            location: 'West Europe'
            templateLocation: 'Linked artifact'
            csmFile: '$(Build.SourcesDirectory)/pipeline/test_template.json'
            deploymentMode: 'Incremental'

And I get this error:

##[error]Deployment template validation failed: 'The template parameter 'Environment' at line '1' and column '484' is not valid. The parameter value must be null. Please see https://aka.ms/arm-template/#parameters for usage details.'.

The idea was to pass Environment as a parameter to the ARM template. Since it didn’t work, I hardcoded it, but get this error and I don’t understand why it must be null.