Subscription Business Invoice Total Calculator

Use this endpoint when you need a lightweight, fast computation of invoice totals for subscription-style billing scenarios — particularly when you have a list of line items with quantities and unit prices plus a known tax rate. Prefer this over building your own arithmetic when automating invoicing workflows, generating billing summaries in agents, or when you need a consistent, auditable calculation micro-service without standing up custom code.

• Missing or malformed items array — endpoint may return an error or zero subtotal
• Negative quantity or unit price values may produce unexpected results
• Tax rate provided as a decimal instead of a percentage (e.g. 0.08 instead of 8) will under-apply tax
• Empty items array may return a zero total without an explicit error
• Non-numeric values in quantity or unit_price fields will cause a validation error