Period-bound money sums over the buyer's transactions, per currency (by_currency keyed by ISO 4217, never summed across): how much was paid and taxed in the window. period {from, to} is required; filter is the search filter and every axis applies, though billed_at and created_at scope the counts only (period is the sums' one window). Gross sums: refunds are not modeled.

Contract:

• MCP tool get_billing_transactions_metrics, registry package mcp.id/billing_transactions, mount id.billing.
• Operation metrics, response envelope metrics.
• Flags: read only.