WebScraping in Powershell with login section

I am trying to 1. Login to my webapp 2. Check for some new rows in a table tag

I have issues with the step 1.

$username = "admin" 
$password = "admin" 
$ie = New-Object -com InternetExplorer.Application 
$ie.visible = $false
$ie.navigate("https://somesite.com") 
while ($ie.ReadyState -ne 4) { start-sleep -m 100 } 
#start-sleep 10
$ie.document.getElementById("login-form-username").value = "$username" 
$ie.document.getElementById("login-form-password").value = "$password" 
$ie.document.getElementById("login").submit()
start-sleep 20 
$ie.Document.body | Out-File -FilePath c:\web.txt 

It opens IE11 and goes to the page. But when it comes to need to findById and input - there is an error: The property 'value' cannot be found on this object. Verify that the property exists and can be set my HTML input section is:

<input name="os_username" class="text medium-field" id="login-form-username" type="text">