How to retrieve a correct token to request Reports on Graph

Hello

I have registered an apps with Reports.Read.All permissions with delegation and Admin Consent
I try to retrieve reports (email, onedrive, ...), but I don't succeed. The token retrieved nerver contains the permission Reports.Read.All

$credentials = Get-Credential

$Uri = "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token"

$Body = @{
grant_type = "client_credentials"
client_id = $ClientId
client_secret = $ClientSecret
scope = 'https://graph.microsoft.com/.default'
redirect_uri = 'https://localhost/'
username = $credentials.GetNetworkCredential().username
password = $credentials.GetNetworkCredential().password
}
$AuthResult = Invoke-RestMethod -Method Post -Uri $uri -ContentType "application/x-www-form-urlencoded" -Body $body

The token has insuffisant rights to call https://graph.microsoft.com/v1.0/reports/getEmailActivityUserDetail(period='D7')

Where is the problem ?

Regards
Gilles