How to Retrieve Secrets from Azure KeyVault in PowerShell?

I'm trying to pull some secrets from an Azure KeyVault for a project involving machine offboarding via Intune. My architect suggested using Azure KeyVault to fetch credentials instead of hardcoding them, which sounds logical to me, but I'm still new to this. While testing my script based on Microsoft's documentation, I'm not getting any output, which makes me think I've messed up somewhere in the access logic. The goal here is to connect using managed identity, but I'm getting a login error when running my script, specifically: "No Azure login detected. Please run 'Connect-AzAccount' to log in." I would appreciate any advice on how to fix this issue or point me in the right direction. Here's the relevant snippet of my script:

```powershell
# OFFBOARDING SCRIPT FOR REMOVING DEVICES NO LONGER OWNED
$ErrorActionPreference = "SilentlyContinue"

# Phase 0: Install required Modules and configure access
Install-Module Az -Force

$tenantId = "tenant-id-guid"
$appId = "client-id-of-managed-identity"
$keyVaultName = "KEYVAULT-NAME"
$resourceGroup = "RESOURCE-GROUP-NAME"
$resourceName = "name-of-managed-identity"
$subId = "subscription-id-that-is-parent-of-resource-group"

Select-AzSubscription -SubscriptionId "$subId"
$identity = Get-AzUserAssignedIdentity -ResourceGroupName "$resourceGroup" -Name "$resourceName"
Connect-AzAccount -Identity -AccountId $identity.ClientId
$keyVault = Get-AzKeyVault -VaultName "$keyVaultName" -ResourceGroupName "$resourceGroup"

if (-not $keyVault) {
Write-Host "Key Vault '$keyVaultName' not found in resource group '$resourceGroup'."
exit
}

# Attempt to retrieve secret
$secret_mut = Get-AzKeyVaultSecret -VaultName $keyVault.VaultName -Name "M-uninstallToken"
```

Any insights would be super helpful!