POSTing data to ServiceNow via Powershell using Invoke-WebRequest - powershell

Question

I am trying to POST information into a table in ServiceNow via a Powershell script. When I run it I get an error
Invoke-WebRequest : The remote server returned an error: (500) Internal Server Error.
Can someone help me figure out how to solve this? Thank you all in advance.
$userName = 'helpMe'
$password = 'iAmStuck' | ConvertTo-SecureString -asPlainText -Force
$cred = New-Object System.Management.Automation.PSCredential($userName, $password)
$uri = 'stuff'
$postParams = "test"
#[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
Invoke-WebRequest -Uri $uri -Method Post -Body $postParams -Credential $cred

Answer 1

ServiceNow has a REST API explorer with various code examples to start working with.
Below is an example that I threw together that posts to the incident table with an admin account. Two important factors here, the user must have roles (here for info https://docs.servicenow.com/bundle/istanbul-servicenow-platform/page/integrate/inbound-rest/reference/r_RESTAPIRoles.html) to use the API and must have access to the table you are trying to post to. Also, note that the body of the post needs to be RAW JSON and all the correct header data is supplied in the URL. If successful ServiceNow will return JSON data about the post.
# Eg. User name="admin", Password="admin" for this code sample.
$user = "admin"
$pass = "noPassword"
# Build auth header
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $user, $pass)))
# Set proper headers
$headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$headers.Add('Authorization',('Basic {0}' -f $base64AuthInfo))
$headers.Add('Accept','application/json')
$headers.Add('Content-Type','application/json')
# Specify endpoint uri
$uri = "https://xxxxx.service-now.com/api/now/table/incident"
# Specify HTTP method
$method = "post"
# Specify request body
{request.body ? "$body = \"" :""}}{\"active\":\"true\",\"number\":\"123\",\"short_description\":\"test\"}"
# Send HTTP request
$response = Invoke-WebRequest -Headers $headers -Method $method -Uri $uri -Body $body
# Print response
$response.RawContent

Answer 2

Even though you posted code, you posted nothing relevant to the problem. Whatever ServiceNow is might have an API for reference on what it's expecting. Often when interacting with web-based APIs, there is a structure that is required for the API to be able to understand the data you're supplying in $postParams. Sometimes it can just be key->value pairs in the case of a flat HTTP POST but often times for RESTful APIs you'll need to structure a JSON header as defined by the API documentation.
If you do a search for "servicenow powershell interaction" it looks like there's a GitHub project for interacting with ServiceNow via PowerShell and also a PDF that specifcally covers this topic.