1. Transaction Data Gets Lost in Translation
Different processors structure transaction data differently. Stripe's metadata fields don't map cleanly to Authorize.Net's custom fields. When you migrate, you need a precise data mapping strategy — not just for current transactions, but for historical data you'll need for reconciliation and refunds.
How to avoid it: Build a full data mapping document before you start. Test it against 100+ real transactions from your old processor to catch edge cases.
2. Recurring Billing Breaks During Cutover
If you have subscriptions or recurring payments, the cutover window is critical. Customers who are charged on the old processor but renewed on the new one can end up double-billed — or worse, not billed at all.
How to avoid it: Run both processors in parallel for one billing cycle. Monitor every recurring charge manually during the transition period.
3. Refunds and Chargebacks Get Orphaned
Refunds issued after migration for transactions processed before migration often fail silently. You think the refund went through — it didn't. The customer calls angry, and you're manually cutting checks.
How to avoid it: Keep API access to your old processor live for 90 days post-migration specifically for refunds and disputes.
4. Compliance and PCI Requirements Change
Different processors have different PCI DSS requirements. Moving from a hosted payment page to an integrated checkout can pull you into PCI SAQ D territory without you realizing it.
How to avoid it: Audit your PCI compliance requirements before you sign the contract with the new processor.
5. Reconciliation Reports Don't Match
Your old processor's settlement reports were formatted one way. Your new processor's are structured completely differently. Your accounting team is now manually reconciling transactions in spreadsheets.
How to avoid it: Build automated reconciliation scripts that normalize both processor formats into a common schema.