Powershell API with HTML table in description

I have trying to create a ticket using API where the description is populated by a variable with the convertto-html.

I am pulling a list of accounts from AD and want to generate a ticket with this information. My code looks like this:

$adaccounts = get-ADUser -* | Select displayname,manager | Convertto-html | Out-String

# Set system parameters - change these details to suit your system environment

$sdphost = "URL"

$techkey = "Key"

# Set API module URL, operation and input data

$url = $sdphost + "sdpapi/request"

$method = "POST"

$operation = "ADD_REQUEST"

$inputdata = @"

{

"operation": {

"details": {

"requester": "AD Reports",

"subject": "Inactive User Accounts",

"description": "$adAccounts",

"requesttemplate": "default",

}

$params = @{INPUT_DATA=$inputdata;OPERATION_NAME=$operation;TECHNICIAN_KEY=$techkey;format='json'}

$result = Invoke-WebRequest -Uri $url -Method $method -Body $params

write-host $result

I keep getting this error:

{"operation":{"result":{"status":"Failed","message":"Error when performing - ADD_REQUEST - Unterminated string at character 332 of {\r\n \\\"operation\\\": {\r\n \\\"details\\\": {\r\n\t\t\t\\\"requester\\\": \\\"AD Reports\\\",\r\n\t\t\t\\\"subject\\\": \\\"Inactive User Accounts\\\",\r\n \\\"description\\\": \\\"