Most ERP integrations fail at the boundary between two teams, not in the code. The storefront team assumes one thing about a field; the SAP team assumes another; the first anyone hears of it is a customer with the wrong invoice.
Contract first
Before we build anything we write the interface contract: every field, its source, its format, what happens when it is missing and who gets alerted. Your SAP team signs it off. The build then implements a document everyone has already agreed to.
Built to be operated
Every message goes through a queue. Every handler is idempotent, so a replay never creates a duplicate order. Failures land in a dead-letter queue with the reason attached, and the audit trail lets support answer “what happened to order 4417?” without asking an engineer.