Maintain a calendar of subscription renewal and customization cutoff dates for each active subscription box; these are typically 3–10 days before the next billing date.
Before each cutoff, fetch the upcoming box contents via the merchant's subscription API and compare against user preferences or a blocklist of unwanted items.
If the box contains unwanted items and the merchant supports item swaps, call the swap endpoint with alternative item preferences before the cutoff deadline.
If the user wants to skip a cycle, call the skip/pause endpoint at least 24 hours before the cutoff to avoid being charged; confirm the skip was registered by fetching the next billing date and verifying it shifted by one cycle.
For cancellation, follow the merchant's cancellation API flow; capture the cancellation confirmation ID and stop all future polling for that subscription.
Log all subscription state changes with timestamps for the user's billing records.
Known gotchas
Subscription box cutoff dates often shift slightly month-to-month; re-fetch the cutoff date from the API each cycle rather than computing it from a fixed offset.
Some subscription platforms require cancellation via a web form rather than an API; if no cancellation API exists, emit a HITL event with deep link and instructions well before the cutoff.
Pausing a subscription on some platforms still charges for the current cycle; confirm whether a pause takes effect immediately or after the current billing period before reporting success to the user.
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