Using GoPhish API in Powershell to Launch Campaigns - powershell

Question

currently i'm attempting to setup GoPhish to launch campaigns through a Windows PowerShell script using it's API. The issue that i'm running into that is i'm getting this error.
Invoke-WebRequest : { "message": "Invalid JSON structure", "success": false, "data": null }
The thing is I have triple checked my JSON structure and it doesn't show any errors in JSON formatting checkers. So my question is if there are any errors in the code I have below for actually pushing these campaigns via PowerShell.
$jsonString = #"
{
"name":"Test6",
"template":{
"name":"Test"
},
"url":"http://redacted",
"page":{
"name":"Test"
},
"smtp":{
"name":"Test SMTP"
},
"launch_date":"2019-25-07T08:20:00+00:00",
"send_by_date":null,
"groups":{
"name":"Test Group"
}
}
"#
Invoke-WebRequest -Uri https://redacted/api/campaigns/?api_key=redacted -Method POST -Body $jsonString
So if you see any errors in what I have an could help me out, that'd be awesome. The API documentation shows that it should be in this format
{
"name":"CC Example Campaign",
"template":{"name":"Example Template"},
"url":"http://localhost",
"page":{"name":"Example Landing Page"},
"smtp":{"name":"Example Sending Profile"},
"launch_date":"2018-10-08T16:20:00+00:00",
"send_by_date":null,
"groups":[{"name":"Example Group"}]
}