# Stripe Subscription Schedule Implementation Lessons

**Last Updated**: February 18, 2026  
**Context**: Deferred promo application for addon quantity changes (v3.1)

## Overview

This document captures critical lessons learned while implementing Stripe Subscription Schedules for deferred promotional discount application. These lessons prevent common pitfalls and ensure proper behavior.

---

## Critical Lesson: `proration_behavior: 'none'` Required at TWO Levels

### Problem Discovered (February 18, 2026)

When updating addon subscription quantity with a deferred 100% FREE promo:
- ✅ Subscription update had `proration_behavior: 'none'` → No immediate charge
- ❌ Subscription Schedule update was MISSING `proration_behavior: 'none'`
- **Result**: Stripe created proration invoices and pending payments despite explicit no-proration setting

### Root Cause

Stripe treats subscription updates and schedule updates as **separate operations**:

1. **Subscription Update** with `proration_behavior: 'none'`:
   - Prevents proration when updating subscription items directly
   - Does NOT affect schedule-initiated changes

2. **Subscription Schedule Update** without `proration_behavior`:
   - Modifying current active phase (changing quantity) **creates proration by default**
   - Completely independent of subscription-level settings
   - Generates draft invoices with proration charges

### Solution

**ALWAYS set `proration_behavior: 'none'` in BOTH places**:

```javascript
// ✅ CORRECT: Set proration_behavior at both levels

// 1. When updating subscription directly
await stripe.subscriptions.update(subscriptionId, {
  items: [{ id: itemId, quantity: newQty }],
  proration_behavior: 'none',  // ← Required for direct updates
  billing_cycle_anchor: 'unchanged'
});

// 2. When updating subscription schedule
await stripe.subscriptionSchedules.update(scheduleId, {
  proration_behavior: 'none',  // ← ALSO Required for schedule changes!
  phases: [
    {
      start_date: currentPhaseStart,
      items: [{ price: priceId, quantity: newQty }],
      end_date: currentPeriodEnd
    },
    {
      items: [{ price: priceId, quantity: newQty }],
      coupon: couponId
    }
  ]
});
```

**Affected Code Locations** (`controllers/subscription.js`):
- ✅ Line 1075: Schedule update when updating existing schedule
- ✅ Line 1114: Subscription update in deferred promo function
- ✅ Line 1136: Schedule update when creating new schedule
- ✅ Line 1899: Subscription update in standard update path

### Verification

After implementing fix, confirmed:
- ✅ No proration invoices created
- ✅ No pending payments generated
- ✅ No customer balance credits
- ✅ Quantity changes immediately with $0.00 transaction
- ✅ Promo applies from next billing period only

---

## Expanded Schedule ID Type Handling

### Problem Discovered (February 18, 2026)

When using `expand: ['data.schedule']` in subscription list calls:
- Stripe returns full schedule **object**, not just ID string
- Passing object to `subscriptionSchedules.update(schedule)` fails:
  - Error: "Argument 'schedule' must be a string, but got: [object Object]"

### Root Cause

Stripe's `expand` parameter changes return value type:
- **Without expand**: `subscription.schedule = "sched_xxx"` (string)
- **With expand**: `subscription.schedule = { id: "sched_xxx", ... }` (object)

APIs like `subscriptionSchedules.update()`, `release()`, `cancel()` expect **string ID only**.

### Solution

**Extract ID before passing to Stripe APIs**:

```javascript
// ✅ CORRECT: Handle both string and expanded object
const scheduleId = typeof subscription.schedule === 'string'
  ? subscription.schedule
  : subscription.schedule.id;

// Use extracted ID in all API calls
await stripe.subscriptionSchedules.update(scheduleId, {...});
await stripe.subscriptionSchedules.release(scheduleId);
await stripe.subscriptionSchedules.cancel(scheduleId);

// BONUS: Reuse expanded object to avoid redundant API call
const scheduleObj = typeof subscription.schedule === 'object'
  ? subscription.schedule  // Already have it!
  : await stripe.subscriptionSchedules.retrieve(scheduleId);
```

**Affected Code Locations** (`controllers/subscription.js`):
- ✅ Lines 1061-1073: Deferred promo function - extract ID and reuse object
- ✅ Lines 1871-1888: Standard update path - extract ID for release/cancel

---

## Subscription Schedule Creation Patterns

### Pattern 1: Create from Existing Subscription (Recommended)

**Use Case**: Adding schedule to subscription that doesn't have one

```javascript
// Step 1: Update subscription quantity (NO proration)
const updatedSub = await stripe.subscriptions.update(subscriptionId, {
  items: [{ id: itemId, quantity: newQty }],
  proration_behavior: 'none',
  billing_cycle_anchor: 'unchanged'
});

// Step 2: Create schedule from subscription
const schedule = await stripe.subscriptionSchedules.create({
  from_subscription: updatedSub.id
  // NOTE: Cannot combine from_subscription + phases in create()
});

// Step 3: Update schedule with phases
await stripe.subscriptionSchedules.update(schedule.id, {
  proration_behavior: 'none',  // ← CRITICAL!
  phases: [
    {
      start_date: schedule.current_phase.start_date,  // Use timestamp from created schedule
      items: [{ price: priceId, quantity: newQty }],
      end_date: currentPeriodEnd
    },
    {
      items: [{ price: priceId, quantity: newQty }],
      coupon: couponId
    }
  ]
});
```

**Why This Pattern**:
- ✅ Preserves subscription state (trial, discount, etc.)
- ✅ Stripe auto-populates first phase from subscription
- ✅ Clean separation of subscription update and schedule management

**Common Mistake**: Trying to combine `from_subscription` + `phases` in `create()` → **Fails!**

### Pattern 2: Update Existing Schedule

**Use Case**: Subscription already has attached schedule

```javascript
// Check if subscription has schedule (may be expanded object or string ID)
if (subscription.schedule) {
  const scheduleId = typeof subscription.schedule === 'string'
    ? subscription.schedule
    : subscription.schedule.id;
  
  const existingSchedule = typeof subscription.schedule === 'object'
    ? subscription.schedule  // Already expanded
    : await stripe.subscriptionSchedules.retrieve(scheduleId);
  
  // Update existing schedule phases
  await stripe.subscriptionSchedules.update(scheduleId, {
    proration_behavior: 'none',  // ← CRITICAL!
    phases: [
      {
        start_date: existingSchedule.current_phase.start_date,
        items: [{ price: priceId, quantity: newQty }],
        end_date: currentPeriodEnd
      },
      {
        items: [{ price: priceId, quantity: newQty }],
        coupon: couponId
      }
    ]
  });
}
```

**Key Points**:
- ✅ Reuse existing schedule instead of creating new one
- ✅ Use `current_phase.start_date` for accurate phase anchoring
- ✅ Handle expanded schedule object to avoid redundant API call

### Pattern 3: Release Schedule for Standard Updates

**Use Case**: Need to update subscription directly (no schedule needed)

```javascript
if (subscription.schedule) {
  const scheduleId = typeof subscription.schedule === 'string'
    ? subscription.schedule
    : subscription.schedule.id;
  
  try {
    // Release subscription from schedule
    await stripe.subscriptionSchedules.release(scheduleId);
  } catch (releaseErr) {
    // Fallback: Cancel schedule if release fails
    try {
      await stripe.subscriptionSchedules.cancel(scheduleId);
    } catch (cancelErr) {
      // Log but don't block - subscription update may still work
    }
  }
}

// Now free to update subscription directly
await stripe.subscriptions.update(subscriptionId, {
  items: [...],
  proration_behavior: 'none'
});
```

**Why Release First**:
- Subscriptions attached to schedules cannot be updated directly
- Error: "cannot migrate a subscription that is already attached to a schedule"
- Releasing detaches schedule and allows direct updates

---

## Phase Configuration Best Practices

### Phase Time Anchoring

**CRITICAL**: Always use actual Unix timestamps for phase boundaries:

```javascript
// ✅ CORRECT
phases: [
  {
    start_date: existingSchedule.current_phase.start_date,  // Unix timestamp
    end_date: subscription.current_period_end,              // Unix timestamp
    items: [...]
  },
  {
    items: [...]  // Next phase starts automatically after previous ends
  }
]

// ❌ WRONG
phases: [
  {
    start_date: 'now',  // String not supported in updates!
    end_date: currentPeriodEnd,
    items: [...]
  }
]
```

### Phase Metadata

**Best Practice**: Add metadata for debugging and tracking:

```javascript
metadata: {
  deferred_promo: 'true',
  promo_coupon: couponId,
  original_quantity: oldQty,
  new_quantity: newQty,
  updated_at: Math.floor(Date.now() / 1000)
}
```

**Why**:
- Helps debug schedule behavior in Stripe dashboard
- Provides audit trail for quantity/promo changes
- Can be used in webhooks for custom logic

---

## Invoice Preview with Schedules

### Dual Invoice Response

When deferred promo detected, return TWO invoices:

```javascript
const response = {
  invoices: [
    {
      // Current period: Quantity change, NO promo
      type: 'current',
      period_type: 'current',
      amount_due: 24975,  // Prorated based on remaining period
      has_promo: false,
      metadata: { period_type: 'current' }
    },
    {
      // Next period: With 100% off promo
      type: 'next',
      period_type: 'next',
      amount_due: 0,
      discount: 24975,
      has_promo: true,
      promo_coupon: 'coup_xxx',
      metadata: {
        period_type: 'next',
        has_promo: 'true',
        promo_coupon: 'coup_xxx'
      }
    }
  ]
};
```

### Preview Parameters for Future Period

**IMPORTANT**: Cannot use `subscription_proration_date` for future period preview:

```javascript
// ❌ WRONG: subscription_proration_date only works for current period
const nextInv = await stripe.invoices.retrieveUpcoming({
  customer: custId,
  subscription: subId,
  subscription_proration_date: nextPeriodStart  // Ignored!
});

// ✅ CORRECT: Create schedule, then preview using schedule_details
const schedule = await stripe.subscriptionSchedules.create({...});
const nextInv = await stripe.invoices.retrieveUpcoming({
  customer: custId,
  schedule: schedule.id
  // Stripe automatically previews next phase
});
```

---

## Common Errors and Solutions

### Error: "cannot migrate a subscription that is already attached to a schedule"

**Cause**: Trying to update subscription directly when it has attached schedule

**Solution**: Release or update schedule instead

```javascript
// Option 1: Release schedule, then update subscription
await stripe.subscriptionSchedules.release(scheduleId);
await stripe.subscriptions.update(subId, {...});

// Option 2: Update schedule phases instead
await stripe.subscriptionSchedules.update(scheduleId, { phases: [...] });
```

### Error: "Argument 'schedule' must be a string, but got: [object Object]"

**Cause**: Passing expanded schedule object to API expecting ID string

**Solution**: Extract ID first (see "Expanded Schedule ID Type Handling" above)

### Unexpected Proration Invoices

**Cause**: Missing `proration_behavior: 'none'` in schedule update

**Solution**: Add to ALL schedule updates that modify current phase:

```javascript
await stripe.subscriptionSchedules.update(scheduleId, {
  proration_behavior: 'none',  // ← Required!
  phases: [...]
});
```

---

## Testing Checklist

When implementing subscription schedules with deferred promos:

- [ ] No proration invoices created when updating quantity
- [ ] No pending payments generated
- [ ] No customer balance credits
- [ ] Quantity changes immediately
- [ ] First phase has NO coupon
- [ ] Second phase HAS coupon
- [ ] Schedule phases have correct start/end dates
- [ ] Invoice preview shows both current and next period
- [ ] Current period invoice amount is $0 (or expected immediate charge)
- [ ] Next period invoice shows 100% discount
- [ ] Metadata properly populated for debugging
- [ ] Schedule ID extraction handles both string and object
- [ ] Release logic works when schedule exists
- [ ] Rejects deferred promo for `cancel_at_period_end: true`

---

## References

- **Implementation**: `controllers/subscription.js` lines 1045-1156 (`updateAddonWithDeferredPromo`)
- **Documentation**: `docs/PROMO_ENHANCEMENTS_V3.md` v3.1 section
- **Test Script**: `tests/test_deferred_promo.js`
- **Stripe Docs**: https://stripe.com/docs/billing/subscriptions/subscription-schedules
- **API Version**: `2025-01-27.acacia`