polar-billing（极地计费）

Polar Billing System

Comprehensive guide to Polar's billing infrastructure, covering entities, flows, Stripe integration, and benefit provisioning.

Quick Reference

Checkout → Payment → Order → Transaction → Benefits
                         ↓
                   Subscription (if recurring)
                         ↓
                   Subscription Cycle → Order → ...

Table of Contents

1. Core Entities
2. Entity Relationships
3. Main Services
4. Dramatiq Background Tasks
5. Stripe Integration
6. Subscription Lifecycle
7. Proration System
8. Benefits & Credits
9. Dunning & Payment Retry
10. Transaction Ledger
11. Key File Locations

1. Core Entities

Checkout

File: server/polar/models/checkout.py

Shopping cart/payment session before order confirmation.

Relationships: organization, customer, product, product_price, discount, subscription (for upgrades)

Order

File: server/polar/models/order.py

Represents a billing event (one-time purchase or subscription cycle).

Computed Properties:

• net_amount = subtotal - discount
• total_amount = net + tax
• due_amount = max(0, total + applied_balance)
• payout_amount = net - platform_fee - refunded

Subscription

File: server/polar/models/subscription.py

Recurring billing relationship.

Relationships: customer, product, payment_method, discount, meters, grants (benefits)

Transaction

File: server/polar/models/transaction.py

All money flows in the system.

Self-referential relationships: payment_transaction, balance_transactions, incurred_transactions

Payment

File: server/polar/models/payment.py

Individual payment transaction.

Refund

File: server/polar/models/refund.py

Customer

File: server/polar/models/customer.py

Product & ProductPrice

Files: server/polar/models/product.py, server/polar/models/product_price.py

BillingEntry

File: server/polar/models/billing_entry.py

Audit log for billing calculations.

2. Entity Relationships

Organization
├── Product
│   ├── ProductPrice (multiple per product)
│   └── ProductBenefit → Benefit
├── Customer
│   ├── Subscription → Product, Discount
│   │   ├── SubscriptionProductPrice
│   │   ├── SubscriptionMeter
│   │   └── BenefitGrant
│   ├── Order → Product, Subscription
│   │   └── OrderItem
│   ├── PaymentMethod
│   └── Wallet
├── Checkout → Customer, Product
├── Discount
│   └── DiscountRedemption
└── Account (for payouts)
    └── Payout → Transaction

Transaction (ledger)
├── payment → Order, Customer
├── refund → Refund, Order
├── dispute → Dispute, Order
├── processor_fee → parent payment
└── payout → Account

3. Main Services

SubscriptionService

File: server/polar/subscription/service.py

Core subscription operations:

# Creation
create_or_update_from_checkout(checkout, payment_method) → (Subscription, created)

# Updates
update_product(subscription, product_id, proration_behavior)
update_seats(subscription, seats, proration_behavior)
update_discount(subscription, discount_id)
update_trial(subscription, trial_end)

# Lifecycle
cycle(subscription)  # Period renewal
cancel(subscription)  # At period end
revoke(subscription)  # Immediately
uncancel(subscription)

# Benefits
enqueue_benefits_grants(task="grant"|"revoke", customer, product)

OrderService

File: server/polar/order/service.py

create_from_checkout(checkout)  # One-time purchase
create_subscription_order(subscription, billing_reason)  # Recurring
trigger_payment(order)  # Charge customer
create_order_balance(order)  # Ledger entries

CheckoutService

File: server/polar/checkout/service.py

create(product, customer_data, discount_code)
confirm(checkout)  # Lock checkout for payment
handle_stripe_success(checkout, charge)
handle_free_success(checkout)  # No payment needed

PaymentService

File: server/polar/payment/service.py

upsert_from_stripe_charge(charge, checkout, order)
handle_success(payment)  # Complete order
handle_failure(payment)  # Update order status

RefundService

File: server/polar/refund/service.py

create(order, amount, reason, revoke_benefits)
upsert_from_stripe(stripe_refund)

BenefitGrantService

File: server/polar/benefit/grant/service.py

enqueue_benefits_grants(task, customer, product, order=None, subscription=None)
grant_benefit(customer, benefit)
revoke_benefit(customer, benefit)

4. Dramatiq Background Tasks

Subscription Tasks

File: server/polar/subscription/tasks.py

Order Tasks

File: server/polar/order/tasks.py

Stripe Webhook Tasks

File: server/polar/integrations/stripe/tasks.py

Benefit Tasks

File: server/polar/benefit/tasks.py

Checkout Tasks

File: server/polar/checkout/tasks.py

Payout Tasks

File: server/polar/payout/tasks.py

5. Stripe Integration

Webhook Endpoints

File: server/polar/integrations/stripe/endpoints.py

• /v1/integrations/stripe/webhook - Direct webhooks
• /v1/integrations/stripe/webhook-connect - Connect account webhooks

Implemented Webhooks

Payment Flow:

• payment_intent.succeeded - Payment complete
• payment_intent.payment_failed - Payment failed
• setup_intent.succeeded - Card saved
• charge.pending/failed/succeeded/updated - Charge lifecycle

Refunds:

• refund.created/updated/failed

Disputes:

• charge.dispute.created/updated/closed

Connect:

• account.updated - Account info changed
• payout.updated/paid - Payout lifecycle

Webhook Processing Flow

Stripe POST → Verify signature → ExternalEvent.enqueue()
                                        ↓
                               Store in external_events table
                                        ↓
                               Enqueue Dramatiq task
                                        ↓
                               Worker processes async
                                        ↓
                               Mark handled_at on success

StripeService

File: server/polar/integrations/stripe/service.py

Key methods:

• create_payment_intent(), create_setup_intent()
• create_refund(), get_refund()
• create_tax_calculation(), create_tax_transaction()
• transfer(), create_payout()

6. Subscription Lifecycle

Creation Flow

1. Checkout created (status=open)
2. Customer completes payment
3. Stripe charge.succeeded webhook
4. payment.handle_success() called
5. checkout_service.handle_stripe_success()
6. subscription_service.create_or_update_from_checkout()
   - Creates Subscription (status=active or trialing)
   - Sets billing period
   - Applies discount
   - Resets meters
7. Enqueue benefit grants
8. Send confirmation email

Cycle Flow (Renewal)

1. APScheduler triggers at period end
2. subscription.cycle task runs
3. subscription_service.cycle()
   - Check cancel_at_period_end
   - If true: set status=canceled, revoke benefits
   - If false: advance period dates, check discount expiry
4. Create billing entry (type=cycle)
5. Enqueue order.create_subscription_order
6. Order created with billing_reason=subscription_cycle
7. Enqueue order.trigger_payment
8. Stripe charges payment method
9. charge.succeeded → ledger entries → benefits renewed

Cancellation Flow

At Period End:

subscription_service.cancel(subscription)
# Sets cancel_at_period_end=True, ends_at=current_period_end
# Benefits remain until period ends
# On next cycle: status=canceled, benefits revoked

Immediately:

subscription_service.revoke(subscription)
# Sets status=canceled, ended_at=now
# Benefits revoked immediately
# Seats canceled if seat-based

Trial Flow

1. Checkout with trial_end set
2. Subscription created with status=trialing
3. No payment during trial
4. At trial_end, cycle task runs
5. Status transitions to active
6. Order created with billing_reason=subscription_cycle_after_trial
7. First payment charged

7. Proration System

When Prorations Occur

1. Product change - Upgrade/downgrade to different tier
2. Seat change - Add/remove seats
3. Interval change - Monthly to yearly

Proration Calculation

# Calculate time remaining in period
pct_remaining = (period_end - now) / (period_end - period_start)

# Old product credit (what they paid but won't use)
old_credit = old_price * old_pct_remaining

# New product debit (what they owe for remainder)
new_debit = new_price * new_pct_remaining

# Net proration
net = new_debit - old_credit

Proration Behaviors

BillingEntry for Prorations

# Credit entry (old product)
BillingEntry(
    type=BillingEntryType.proration,
    direction=BillingEntryDirection.credit,
    amount=prorated_old_amount
)

# Debit entry (new product)
BillingEntry(
    type=BillingEntryType.proration,
    direction=BillingEntryDirection.debit,
    amount=prorated_new_amount
)

Seat Proration

# Adding 2 seats at $10/seat with 50% time remaining
delta_amount = 2 * $10 * 0.5 = $10

BillingEntry(
    type=BillingEntryType.subscription_seats_increase,
    direction=BillingEntryDirection.debit,
    amount=1000  # cents
)

8. Benefits & Credits

Benefit Types

Benefit Grant Flow

1. Order/Subscription created
2. enqueue_benefits_grants(task="grant")
3. For each benefit in product:
   - Skip if already granted
   - Enqueue benefit.grant task
4. benefit.grant task:
   - Get/create BenefitGrant record
   - Call strategy.grant() (type-specific)
   - Set granted_at
   - Store properties
   - Send webhook

Benefit Revocation Flow

1. Subscription canceled or order refunded
2. enqueue_benefits_grants(task="revoke")
3. For each granted benefit:
   - Enqueue benefit.revoke task
4. benefit.revoke task:
   - Call strategy.revoke() (type-specific)
   - Set revoked_at
   - Send webhook

Meter Credits

Grant:

# Create event with units
Event(type="meter_credited", units=100)
# Update CustomerMeter

Cycle (renewal):

# Calculate rollover
rollover = min(remaining_units, rollover_limit)
# Reset meter
Event(type="meter_reset")
# Credit new period + rollover
Event(type="meter_credited", units=base_units + rollover)

Revoke:

# Negative credit event
Event(type="meter_credited", units=-remaining_units)

Grace Period

Organizations can configure benefit_revocation_grace_period (days) to delay benefit revocation for past_due subscriptions.

9. Dunning & Payment Retry

Dunning Process

1. order.process_dunning runs hourly
2. Finds orders where next_payment_attempt_at <= now
3. For each order:
   - Enqueue order.process_dunning_order
4. process_dunning_order:
   - Get customer's payment method
   - Attempt payment via Stripe
   - On success: mark order paid
   - On failure: schedule next attempt

Retry Schedule

Configured in organization settings. Typical pattern:

• Day 1: First failure
• Day 3: Retry 1
• Day 5: Retry 2
• Day 7: Final retry, then mark unpaid

Subscription Status During Dunning

payment fails → status=past_due, past_due_at=now
               ↓
         benefits may continue (grace period)
               ↓
         retry succeeds → status=active
               ↓
         retry fails → status=unpaid, benefits revoked

10. Transaction Ledger

Transaction Types

Creating Payment Transactions

1. charge.updated webhook (charge settled)
2. Get balance_transaction from Stripe
3. Extract settlement amount and fees
4. Create Transaction(type=payment)
5. Enqueue processor_fee.create_payment_fees
6. Create Transaction(type=processor_fee)

Payout Flow

1. Creator has balance from transactions
2. payout.trigger_stripe_payouts (daily)
3. Calculate available balance
4. Create Payout record
5. stripe_service.transfer() to Connect account
6. stripe_service.create_payout() to bank
7. payout.paid webhook → update status

11. Key File Locations

Models

server/polar/models/
├── checkout.py
├── order.py
├── order_item.py
├── subscription.py
├── subscription_product_price.py
├── transaction.py
├── payment.py
├── refund.py
├── dispute.py
├── payout.py
├── customer.py
├── product.py
├── product_price.py
├── discount.py
├── benefit.py
├── benefit_grant.py
└── billing_entry.py

Services

server/polar/
├── subscription/service.py
├── order/service.py
├── checkout/service.py
├── payment/service.py
├── refund/service.py
├── dispute/service.py
├── payout/service.py
├── benefit/
│   ├── service.py
│   ├── grant/service.py
│   └── strategies/
│       ├── meter_credit/service.py
│       ├── github_repository/service.py
│       ├── discord/service.py
│       └── ...
└── transaction/service/
    ├── payment.py
    ├── refund.py
    └── dispute.py

Background Tasks

server/polar/
├── subscription/tasks.py
├── order/tasks.py
├── checkout/tasks.py
├── benefit/tasks.py
├── payout/tasks.py
└── integrations/stripe/tasks.py

Stripe Integration

server/polar/integrations/stripe/
├── endpoints.py    # Webhook handlers
├── service.py      # Stripe API wrapper
├── tasks.py        # Webhook processing tasks
└── payment.py      # Payment resolution helpers

Common Debugging Scenarios

Payment Failed

1. Check Payment record for decline_reason
2. Check Order.status and next_payment_attempt_at
3. Look at external_events for Stripe webhook

Benefits Not Granted

1. Check BenefitGrant record for errors
2. Look at benefit.grant task in Dramatiq logs
3. Verify product has benefits attached

Proration Issues

1. Check BillingEntry records for subscription
2. Verify billing_reason on Order
3. Check subscription's current_period dates

Subscription Not Cycling

1. Check scheduler_locked_at on subscription
2. Verify APScheduler is running
3. Check subscription.cycle task logs