✔ Define source-of-truth rules before any development begins: Document which system is authoritative for each data domain. A simple example: ERP owns vendor payment terms and financial account codes; Coupa owns purchase order approval status and requisition details.

✔ Establish approval workflows across systems: Vendor requests created in Coupa should require ERP validation before activation. This single governance rule eliminates the majority of duplicate supplier conflicts.

✔ The hidden cost of skipping this: When a required GL code is missing in the ERP, Coupa invoice syncs fail silently. If no one notices for 48–72 hours, a payment backlog forms. Discovered at month-end, that backlog becomes a finance and audit crisis.

✔ Treat integration as a system, not a one-off task: Even if your initial scope is limited, define an integration architecture document before development begins. Decide whether you will use an iPaaS platform (Celigo, Dell Boomi, MuleSoft), a middleware layer, or a direct API strategy — and document transformation logic, error handling, and monitoring within that framework.

✔ The scalability test: Ask your integration lead this question before go-live — "If we add one more system next year, how many things break?" If the answer is "several," your architecture is already brittle.

✔ Middleware pays for itself: The upfront cost of a proper integration platform feels like overhead. The cost of rebuilding a spaghetti architecture 18 months post-launch — with production data at stake — is exponentially higher.

✔ Conduct dedicated field mapping sessions for every critical object: For each entity — purchase orders, invoices, receipts, supplier records — list every field, its source value in Coupa, its target field in the ERP, and any transformation logic required. This is not a spreadsheet to be completed in an afternoon; it is a design deliverable.

✔ Required ERP fields are non-negotiable: If the ERP requires an asset category, company code, or expense type that Coupa does not capture by default, that gap must be resolved in the design phase — through a default value, a business rule, or a new Coupa field — not discovered when payments start failing.

✔ Phase your field scope deliberately: Start with the highest-volume, highest-risk fields for launch. Document lower-priority fields as a governed backlog for a subsequent phase. This narrows testing complexity without creating unmaintained technical debt.

✔ Design test cases for the scenarios that break things: Cancelled POs, backdated orders, partial receipts, duplicate submissions, missing required fields, out-of-sequence approvals. If your test plan does not include these, your go-live is your real test.

✔ Regression testing is not optional after updates: Coupa releases quarterly updates. SAP and NetSuite do the same. Any release can introduce new required fields, changed API behaviors, or deprecated endpoints. Without a sandbox regression cycle tied to each update, a previously stable integration can break silently in production.

✔ Schedule testing time that doesn't compete with month-end close: The most common reason UAT is underpowered is that it was scheduled during the period when finance teams are least available. Plan testing windows explicitly and protect them.

✔ Build retry logic for transient failures: Network blips and temporary ERP locks are recoverable errors. Your integration should automatically retry these a defined number of times before escalating to a human — not immediately drop the transaction.

✔ Assign a named owner for every error type: If a Coupa invoice fails due to a missing cost center, the system should notify a designated AP contact with the transaction details and a clear path to correct and resubmit. "IT will handle it" is not an ownership model.

✔ A dashboard is not optional: Post-launch, someone must be able to see at any moment how many transactions are stalled, which error codes are appearing, and how long records have been in a failed state. If your integration has no operational visibility, you are flying blind.

✔ Include error handling in your go-live definition: An integration is not go-live ready if it cannot fail gracefully. Build this into your acceptance criteria, not your phase-two backlog.