Invoke-PnPSPRestMethod - V2.1 API Shares Folder - Accept Header Cannot be Satisfied

[albergsma]

I am using Invoke-PnPSPRestMethod to download the contents of a thumbnail image file (for SPO News articles). SharePoint looks to be storing the image in a link similar to below (shortened for simplicity)

$url1 = https://tenant.sharepoint.com/_api/v2.1/shares/.../driveItem/thumbnails/0/c400x99999/content?preferNoRedirect=true"

Using the following
$output = Invoke-PnPSPRestMethod -url1 $picFile -ContentType 'application/octet-stream'

I get the following error.
Message : {"error":{"code":"notAcceptable","message":"Accept header cannot be satisfied (Accept: 'application/json; odata=nometadata', Content-Type: 'image/png')"}}

I am able to retrieve content with the following (removed the redirect at end of the link)

$url2 = https://tenant.sharepoint.com/_api/v2.1/shares/.../driveItem/thumbnails/0/c400x99999/content"
$output = Invoke-PnPSPRestMethod -url $url2 -Raw
$output | Out-File -FilePath C:\temp\pic.png

In this case the pic.png is not recognizeable as image (is 125KB, vs the actual image is 49 KB).

Any ideas?