Help with Invoke-WebRequest and Basic Auth Error

I'm trying to use Invoke-WebRequest for retrieving an Auth Token, but I'm running into an error that says:

Invoke-RestMethod:
{
"message": "Authorization header requires 'Credential' parameter. Authorization header requires 'Signature' parameter. Authorization header requires 'SignedHeaders' parameter. Authorization header requires existence of either a 'X-Amz-Date' or a 'Date' header. (Hashed with SHA-256 and encoded with Base64) Authorization=.REDACTED"
}

I thought Invoke-WebRequest could handle Basic Auth since .NET 6 Core, so I'm wondering if I'm missing something or if this might be a bug. I've tested it in two ways: first, by generating headers manually using the older method, and second, by using the newer approach that supplies the credential. I checked that both manually created and automatically generated headers match, so it doesn't seem to be an issue there.

Here's my code snippet for clarity:

$test = $authClientID+":"+$authSecret
$auth = [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes($test))
$secretIN = ConvertTo-SecureString $authSecret -AsPlainText
$headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$headers.Add("Authorization","Basic "+$auth)
$cred = New-Object System.Management.Automation.PSCredential($authClientID, $secretIN)
$body = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$body.Add("grant_type","client_credentials")
$body.Add("scope","read")
$webResponse0 = Invoke-RestMethod -Uri $tokenRequestUrl -Body $body -SessionVariable myRequest0 -Authentication Basic -Credential $cred
$webResponse1 = Invoke-RestMethod -Uri $tokenRequestUrl -Body $body -SessionVariable myRequest1 -Headers $headers -Method POST
$myRequest0.Headers.Authorization -eq $myRequest1.Headers.Authorization