blah.ps1

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# Generate or retrieve the API key - Log in to the Enterprise portal and follow the tutorial 
# under Help - Reporting APIs. The first section under this help article explains how to 
# generate or retrieve the API key for the specified enrollment.
# Source: https://docs.microsoft.com/en-us/azure/billing/billing-enterprise-api
#
# Endpoints and sample responses are here: 
#      https://docs.microsoft.com/en-us/rest/api/billing/enterprise/billing-enterprise-api-usage-detail#json-format
# You can use that documentation to help understand the key/values returned.
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$resource = "https://consumption.azure.com/v2/enrollments/YOUR_ENROLLMENT_NUMBER_HERE/usagedetails"
$result = Invoke-RestMethod -Method Get -Uri $resource -Header @{ "Authorization" = "bearer YOUR_API_KEY_HERE" }

Write-Output ("REST Call Result: '$($result)'")