InvoiceAgent: Bulletproof AI for Ad Spend Invoices

Client faced a major bottleneck processing complex Japanese Google Ads invoices because manual entry was slow and missed negative line items. The author built a hybrid n8n solution routing simple items to code and complex negatives to Claude 3.5 Sonnet, enforcing structured outputs, fuzzy-matching projects, and syncing results to Google Sheets and a Board API, cutting processing time to minutes and saving about $2000/month.