API auth REST vs SOAP

[BBagent]

I'm having an issue authenticating via RESTful API, PAN OS version 11.1

Using SOAP to fetch my API key, then storing it here

$header = @{
"X-PAN-KEY" = $apikey
}

Then Invoke-Restmethod like this

Invoke-RestMethod -Uri $newURI -Method get -ContentType "application/json" -Headers $header

URI is https://ip_address/restapi/v11.1/Device/VirtualSystems

error message

Invoke-RestMethod : {"code":7,"message":"Unauthorized","details":[{"@type":"CauseInfo","causes":[{"code":5,"module":"panui_auth","description":"Unauthorized"}]}]}

I don't have any trouble pulling that data when I use SOAP like this

/api?key=$apikey&type=op&cmd=<show><devices><connected></connected></devices></show>