Get value from JSON using string from array [duplicate]

The best way of resolving nested properties is to resolve them one at a time :)

A simpler example, for retrieving just one value:

$json = '{"root":{"branch":{"setting1":"Value 1","setting2":"Value 2","setting3":"Value 3"}}}' |ConvertFrom-Json

# define the "path" to the value we want
$path = 'root.branch.setting1'

# split path into individual property names
$path = $path.Split('.')

# start from the root object and then start "walking" down the object hierarchy
$cursor = $json
foreach($property in $path)
{
  # advance cursor one level deeper
  $cursor = $cursor.$property
}

# this will now contain "Value 1"
$cursor

You can turn this into a neat little function:

function Resolve-MemberChain 
{
  param(
    [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
    [psobject[]]$InputObject,

    [Parameter(Mandatory = $true, Position = 0)]
    [string[]]$MemberPath,

    [Parameter(Mandatory = $false)]
    [string]$Delimiter
  )

  begin {
    if($PSBoundParameters.ContainsKey('Delimiter')){
      $MemberPath = $MemberPath.Split([string[]]@($Delimiter))
    }
  }

  process {
    foreach($obj in $InputObject){
      $cursor = $obj
      foreach($member in $MemberPath){
        $cursor = $cursor.$member
      }
    
      $cursor
    }
  }
}

Then use it like this:

$json |Resolve-MemberChain 'root.branch.setting1' -Delimiter '.'

Or, as in your case, within a calculated property expression, like so:

$AccountService.GetEnumerator()|%{
  $path = $_.Key
  $json |Select @{Name='Val';Expression={$_ |Resolve-MemberChain $path -Delimiter .}} 
}