Operator context
Longer answer
Double-billing during subscription migration is the most common customer-facing incident in the cutover week and the most preventable. The mechanic is straightforward: active subscribers have in-flight billing cycles, and if both the source platform and Shopify process the same cycle, the customer gets charged twice. The discipline that prevents it is explicit cutover sequencing.
The first move is choosing a cutover date that aligns with the lowest-volume billing window for the active subscriber base. Most brands have a billing concentration on the 1st or 15th of the month; cut over in the days immediately after a cycle completes to maximise the runway before the next billing event. Brands that cut over mid-cycle handle more billing edge cases than brands that cut over between cycles.
The second move is the hard sequencing rule: disable subscription billing on the source platform first, validate the disable (confirm via the source app that scheduled charges have stopped), then enable on Shopify. The order matters because reversing it produces an overlap window where both systems can process the same cycle. The validation step is what catches imperfect source-platform disabling.
The third move is payment-processor coordination. Stripe, Braintree, or whichever processor handles charges needs advance notice of the migration because customer-of-record tokens often change. The processor's relationship manager (every $5M+ brand has one) should be looped into the cutover runbook two to four weeks before launch.
The fourth move is real-time monitoring of the first post-migration billing cycle. Brands that staff a dedicated subscription-cutover monitor for the first week catch billing issues fast enough to refund proactively rather than reactively. Brands that monitor casually consistently let small billing issues become customer-facing incidents that compound into trust damage and elevated churn.