Azure pipeline task: ManualValidation passing parameter into input

I've tried many variations but without success.

I am trying to achieve this functionality but using a parameter of emai addresses and groups:

This works:

steps:
      - task: ManualValidation@0
        timeoutInMinutes: 1440 # task times out in 1 day 
        inputs:
          onTimeout: reject
          notifyUsers: |
            [muttsMitts]\release_group
            admin@muttsMitts.com
          instructions: 'Please validate the build configuration and resume'

With parameter
Creating a string as a variable, looping, passing just the original object.

parameters:
  - name: 'emailList'
    type: object
    default:
      - '[muttsMitts]\release_group' # I have to put the quotes around the string
      - [muttsMitts]\release_group

 - job: manual_approval
      displayName: "Manual Approval"
      pool: server
      timeoutInMinutes: 4320 # job times out in 3 days
      variables:
        - name: emailList
          value: ${{join(', ', parameters.emailList)}}
      steps:
      - task: ManualValidation@0
        timeoutInMinutes: 1440 # task times out in 1 day 
        inputs:
          onTimeout: reject
          notifyUsers: |
            ${{each email in parameters.emailList}}
              ${{email}}
          instructions: 'Please validate the build configuration and resume'

Returns error:

Encountered error(s) while parsing pipeline YAML:
/azure-pipelines.yml (Line: 96, Col: 24): The directive 'each' is not allowed in this context. Directives are not supported for expressions that are embedded within a string. Directives are only supported when the entire value is an expression.

You could always use a string and just pass through the parameter value.

In your reusable job, just define a string parameter:

# job.yaml
parameters:
- name: notifyUsers
  type: string
  default: ''

jobs:
- job: manual_approval
  displayName: Manual Approval
  pool: server
  timeoutInMinutes: 4320 # job times out in 3 days
  steps:
  - task: ManualValidation@0
    timeoutInMinutes: 1440 # task times out in 1 day 
    inputs:
      onTimeout: reject
      notifyUsers: ${{ parameters.notifyUsers }}
      instructions: Please validate the build configuration and resume

Then you can invoke it like that:

jobs:
- template: ./job.yaml
  parameters:
    notifyUsers: |
      [muttsMitts]\release_group
      admin@muttsMitts.com

If you'd like to use an array, your approach works. you just need to have a join on line break:

# job.yaml
parameters:
- name: notifyUsers
  type: object
  default: []

jobs:
- job: manual_approval
  displayName: Manual Approval
  pool: server
  timeoutInMinutes: 4320 # job times out in 3 days
  steps:
  - task: ManualValidation@0
    timeoutInMinutes: 1440 # task times out in 1 day 
    inputs:
      onTimeout: reject
      notifyUsers: ${{ join('\n', parameters.notifyUsers) }}
      instructions: Please validate the build configuration and resume

Then invoke it like that:

resources:
- repo: self

trigger: none
pr: none

jobs:
- template: ./job.yaml
  parameters:
    notifyUsers:
    - '[muttsMitts]\release_group'
    - 'admin@muttsMitts.com'