Cannot connect to RC api using powershell

Cannot connect to API using my powershell script. It looks like it connects but then when it starts running through the AD portion of my script it errors out with this error:

t C:PSAutomationsRCUpdateInfoV3-test.ps1:36 char:17
+ ... $userinfo = Get-ADUser -Filter "UserPrincipalName -eq '$email'" -prop ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Get-ADUser], ADException
    + FullyQualifiedErrorId : ActiveDirectoryServer:8254,Microsoft.ActiveDirectory.Management.Commands.GetADUser
 
Invoke-RestMethod : {
  "message": "Need Content-Type header"

Full Script:

$RC_SERVER_URL="https://platform.ringcentral.com"
$RC_CLIENT_ID="Yxxxxxx"
$RC_CLIENT_SECRET="xxxxxx"
$RC_JWT_TOKEN = "xxxxxxxx"

$headers = @{
    ContentType = 'application/x-www-form-urlencoded; charset=UTF-8'
    Accept = 'application/json'
    Authorization = 'Basic ' + [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("${RC_CLIENT_ID}:${RC_CLIENT_SECRET}"))
}

# RC authenticate and obtain access token
$response = Invoke-RestMethod -Method POST -Uri ($RC_SERVER_URL + "/restapi/oauth/token") -Headers $headers -Body @{
    grant_type = 'urn:ietf:params:oauth:grant-type:jwt-bearer'
    assertion = $RC_JWT_TOKEN
}

# Extyract Access Token
$access_token = $response.access_token

# Fetch User info from RC api
$AllUsers = Invoke-RestMethod ($RC_SERVER_URL + "/restapi/v1.0/account/~/extension/?perPage=1000") -Headers @{
    Authorization = "Bearer $access_token"
} -Method Get

# Array to store users with AD information
$UsersArray = @()

#import AD Module
Import-Module ActiveDirectory

# Iterating over user records
foreach ($id in $AllUsers.records) {
    $email = $id.contact.email
    # Retrieving AD user information using email
    $userinfo = Get-ADUser -Filter "UserPrincipalName -eq '$email'" -properties department, title
    $emailCheck = $userinfo.UserPrincipalName

    if ($emailcheck -ne $null -and $id.type -ne "Department") { 
        $department = $userinfo.department
        $jobtitle = $userinfo.title
      
        $UsersArray += @(
            @{
                id = $id.id
                email = $id.contact.email
                department = $department
                jobtitle = $jobtitle
            }
        )
    } 
}

# Iterating over users and updating profiles
foreach ($user in $UsersArray) {
    $did = $user.id
    $putbody = '{"contact": {"jobTitle":"' + $user.jobtitle + '"}}'
    Invoke-RestMethod ($RC_SERVER_URL + "/restapi/v1.0/account/~/extension/$did") -Headers @{
        Authorization = "Bearer $access_token"
        ContentType = 'application/json'  # Add Content-Type header
    } -Method PUT -Body $putbody
    
    $putdepartment = '{"contact": {"department":"' + $user.department + '"}}'
    Invoke-RestMethod ($RC_SERVER_URL + "/restapi/v1.0/account/~/extension/$did") -Headers @{
        Authorization = "Bearer $access_token"
        ContentType = 'application/json'  # Add Content-Type header
    } -Method PUT -Body $putdepartment

    Start-Sleep -Seconds 3
    $did = $null
}