A PowerShell function for querying one or more AppInsights accounts (or all AppInsights accounts under a subscription once logged in) to get the daily cap setting and previous 24 hours of usage

Get-AppInsightsUsage.ps1

Function Get-AppInsightsUsage {

    Param(
        # Optional: One or more AppInsights resource names
        [string[]]
        $Name
    )

    $AppInsights = Get-AzApplicationInsights
    If ($Name) { $AppInsights = $AppInsights | Where-Object { $_.Name -in $Name } }

    ForEach ($AI in $AppInsights) {
        $DailyCap = Set-AzureRmApplicationInsightsDailyCap -ResourceGroupName $AI.ResourceGroupName -Name $AI.Name

        $Permissions = @('ReadTelemetry', 'WriteAnnotations')
        $APIKey = New-AzApplicationInsightsApiKey -ResourceGroupName $AI.ResourceGroupName -Name $AI.Name -Permissions $Permissions -Description 'GetAppInsightsUsageKey'
        $AppId = $AI.AppId

        $Headers = @{ 
            'X-Api-Key'    = $APIKey.ApiKey
            'Content-Type' = 'application/json' 
        }

        $Query = 'systemEvents
            | where timestamp >= ago(24h)
            | where type == "Billing"
            | extend BillingTelemetryType = tostring(dimensions["BillingTelemetryType"])
            | extend BillingTelemetrySizeInBytes = todouble(measurements["BillingTelemetrySize"])
            | summarize sum(BillingTelemetrySizeInBytes)'

        $EscapedQuery = [uri]::EscapeUriString("?query=$Query")

        $Result = Invoke-RestMethod -uri "https://api.applicationinsights.io/v1/apps/$AppId/query$EscapedQuery" -Headers $Headers

        $Usage = [Math]::Round($Result.tables.rows[0] / 1GB, 2)

        Remove-AzApplicationInsightsApiKey -ApiKeyId $APIKey.Id -ResourceGroupName $AI.ResourceGroupName -Name $AI.Name

        [pscustomobject]@{
            Name          = $AI.Name
            ResourceGroup = $AI.ResourceGroupName
            DailyCap      = $DailyCap.Cap
            Usage         = $Usage
        }
    }
}