JIRA Cloud API GET Request - Works in Postman, but not Powershell - powershell

Question

I am able to perform a GET Request from Jira successfully in Postman, but am unable to make the same request in Powershell due to an authentication error. I know that my credentials are correct because there are or GET Requests that are successful. My guess is that it has something to do with the URL (https://arnold.jira.com/admin/rest/um/1/user).
Since I know that my credentials are correct, I am not sure what else I can try.
# Create a new session using the Jira REST API
$user = 'john.rambo#arnold.com'
$pass = '8675309'
$pair = "$($user):$($pass)"
$encodedCreds = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes($pair))
$basicAuthValue = "Basic $encodedCreds"
$Headers = #{
Authorization = $basicAuthValue;
Accept = 'application/json'
}
# Perform the GET Request
$UserEmail = 'dolf.lundgren#arnold.com'
$UserAttributeLink = 'https://arnold.jira.com/admin/rest/um/1/user?email=' + $UserEmail + '&expand=attributes'
$UserAttributes = Invoke-RestMethod ($UserAttributeLink) -Headers $Headers -Method GET -ContentType "application/json"
I expect to have the info returned, but am met with this error:
Invoke-RestMethod : User failed to authenticate
At line:12 char:19
+ ... ttributes = Invoke-RestMethod ($UserAttributeLink) -Headers $Headers ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (Method: GET, Reques\u2026PowerShell/6.2.1
}:HttpRequestMessage) [Invoke-RestMethod], HttpResponseException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand