Sage Sage Purchase Invoices API Purchase invoice and supplier bill management Documentation GitHub OpenAPI Documentation 📖 Documentation https://developer.sage.com/accounting/reference 📖 GettingStarted https://developer.sage.com/accounting/guides/concepts/overview Specifications ⚙ OpenAPI https://raw.githubusercontent.com/api-evangelist/sage/refs/heads/main/openapi/sage-purchase-invoices-api-openapi.yml