stripe-integration-expert

name

stripe-integration-expert

description

Production-grade Stripe integrations: subscriptions with trials and proration, one-time payments, usage-based billing, checkout sessions, idempotent webhook handlers, customer portal, and invoicing. Covers Next.js, Express, and Django patterns. Use when integrating Stripe for the first time, debugging webhook reliability issues, migrating from a different payment provider, or adding usage-based billing to an existing subscription product.

Stripe Integration Expert

Tier: POWERFUL
Category: Engineering Team
Domain: Payments / Billing Infrastructure

---

Overview

Implement production-grade Stripe integrations: subscriptions with trials and proration, one-time payments, usage-based billing, checkout sessions, idempotent webhook handlers, customer portal, and invoicing. Covers Next.js, Express, and Django patterns.

---

Core Capabilities

• Subscription lifecycle management (create, upgrade, downgrade, cancel, pause)
• Trial handling and conversion tracking
• Proration calculation and credit application
• Usage-based billing with metered pricing
• Idempotent webhook handlers with signature verification
• Customer portal integration
• Invoice generation and PDF access
• Full Stripe CLI local testing setup

---

When to Use

• Adding subscription billing to any web app
• Implementing plan upgrades/downgrades with proration
• Building usage-based or seat-based billing
• Debugging webhook delivery failures
• Migrating from one billing model to another

---

Subscription Lifecycle State Machine

FREE_TRIAL ──paid──► ACTIVE ──cancel──► CANCEL_PENDING ──period_end──► CANCELED
     │                  │                                                    │
     │               downgrade                                            reactivate
     │                  ▼                                                    │
     │             DOWNGRADING ──period_end──► ACTIVE (lower plan)           │
     │                                                                        │
     └──trial_end without payment──► PAST_DUE ──payment_failed 3x──► CANCELED
                                          │
                                     payment_success
                                          │
                                          ▼
                                        ACTIVE

DB subscription status values:

trialing | active | past_due | canceled | cancel_pending | paused | unpaid

---

Stripe Client Setup

// lib/stripe.ts
import Stripe from "stripe"

export const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!, {
  apiVersion: "2024-04-10",
  typescript: true,
  appInfo: {
    name: "myapp",
    version: "1.0.0",
  },
})

// Price IDs by plan (set in env)
export const PLANS = {
  starter: {
    monthly: process.env.STRIPE_STARTER_MONTHLY_PRICE_ID!,
    yearly: process.env.STRIPE_STARTER_YEARLY_PRICE_ID!,
    features: ["5 projects", "10k events"],
  },
  pro: {
    monthly: process.env.STRIPE_PRO_MONTHLY_PRICE_ID!,
    yearly: process.env.STRIPE_PRO_YEARLY_PRICE_ID!,
    features: ["Unlimited projects", "1M events"],
  },
} as const

---

Checkout Session (Next.js App Router)

// app/api/billing/checkout/route.ts
import { NextResponse } from "next/server"
import { stripe } from "@/lib/stripe"
import { getAuthUser } from "@/lib/auth"
import { db } from "@/lib/db"

export async function POST(req: Request) {
  const user = await getAuthUser()
  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 401 })

  const { priceId, interval = "monthly" } = await req.json()

  // Get or create Stripe customer
  let stripeCustomerId = user.stripeCustomerId
  if (!stripeCustomerId) {
    const customer = await stripe.customers.create({
      email: user.email,
      name: "username-undefined"
      metadata: { userId: user.id },
    })
    stripeCustomerId = customer.
     db..({ : { : user. }, : { stripeCustomerId } })
  }

   session =  stripe...({
    : stripeCustomerId,
    : ,
    : [],
    : [{ : priceId, :  }],
    : ,
    : {
      : user. ?  : ,
      : { : user. },
    },
    : ,
    : ,
    : { : user. },
  })

   .({ : session. })
}

---

Subscription Upgrade/Downgrade

// lib/billing.ts
export async function changeSubscriptionPlan(
  subscriptionId: string,
  newPriceId: string,
  immediate = false
) {
  const subscription = await stripe.subscriptions.retrieve(subscriptionId)
  const currentItem = subscription.items.data[0]

  if (immediate) {
    // Upgrade: apply immediately with proration
    return stripe.subscriptions.update(subscriptionId, {
      items: [{ id: currentItem.id, price: newPriceId }],
      proration_behavior: "always_invoice",
      billing_cycle_anchor: "unchanged",
    })
  } else {
    // Downgrade: apply at period end, no proration
    return stripe.subscriptions.update(subscriptionId, {
      items: [{ id: currentItem.id, price: newPriceId }],
      proration_behavior: "none",
      billing_cycle_anchor: "unchanged",
    })
  }
}

// Preview proration before confirming upgrade
export async  () {
   subscription =  stripe..(subscriptionId)
   prorationDate = .(.() / )

   invoice =  stripe..({
    : subscription.  ,
    : subscriptionId,
    : [{ : subscription..[]., : newPriceId }],
    : prorationDate,
  })

   {
    : invoice.,
    prorationDate,
    : invoice..,
  }
}

---

Complete Webhook Handler (Idempotent)

// app/api/webhooks/stripe/route.ts
import { NextResponse } from "next/server"
import { headers } from "next/headers"
import { stripe } from "@/lib/stripe"
import { db } from "@/lib/db"
import Stripe from "stripe"

// Processed events table to ensure idempotency
async function hasProcessedEvent(eventId: string): Promise<boolean> {
  const existing = await db.stripeEvent.findUnique({ where: { id: eventId } })
  return !!existing
}

async function markEventProcessed(eventId: string, type: string) {
  await db.stripeEvent.create({ data: { id: eventId, type, processedAt: new Date() } })
}

export async  () {
   body =  req.()
   signature = ().()!

   : .
   {
    event = stripe..(body, signature, process..!)
  }  (err) {
    .(, err)
     .({ :  }, { :  })
  }

  
   ( (event.)) {
     .({ : , :  })
  }

   {
     (event.) {
       :
         (event..  ..)
        

       :
       :
         (event..  .)
        

       :
         (event..  .)
        

       :
         (event..  .)
        

       :
         (event..  .)
        

      :
        .()
    }

     (event., event.)
     .({ :  })
  }  (err) {
    .(, err)
    
     .({ :  }, { :  })
  }
}

  () {
   (session. !== ) 
  
   userId = session.?.
   (!userId)   ()

   subscription =  stripe..(session.  )
  
   db..({
    : { : userId },
    : {
      : session.  ,
      : subscription.,
      : subscription..[]..,
      :  (subscription. * ),
      : subscription.,
      : ,
    },
  })
}

  () {
   user =  db..({
    : { : subscription. },
  })
   (!user) {
    
     customer =  db..({
      : { : subscription.   },
    })
     (!customer)   ()
  }

   db..({
    : { : subscription. },
    : {
      : subscription..[]..,
      :  (subscription. * ),
      : subscription.,
      : subscription.,
    },
  })
}

  () {
   db..({
    : { : subscription. },
    : {
      : ,
      : ,
      : ,
      : ,
    },
  })
}

  () {
   (!invoice.) 
   attemptCount = invoice.
  
   db..({
    : { : invoice.   },
    : { :  },
  })

   (attemptCount >= ) {
    
     (invoice.!, )
  }  {
     (invoice.!, )
  }
}

  () {
   (!invoice.) 

   db..({
    : { : invoice.   },
    : {
      : ,
      :  (invoice. * ),
    },
  })
}

---

Usage-Based Billing

// Report usage for metered subscriptions
export async function reportUsage(subscriptionItemId: string, quantity: number) {
  await stripe.subscriptionItems.createUsageRecord(subscriptionItemId, {
    quantity,
    timestamp: Math.floor(Date.now() / 1000),
    action: "increment",
  })
}

// Example: report API calls in middleware
export async function trackApiCall(userId: string) {
  const user = await db.user.findUnique({ where: { id: userId } })
  if (user?.stripeSubscriptionId) {
    const subscription = await stripe.subscriptions.retrieve(user.stripeSubscriptionId)
    const meteredItem = subscription.items.data.find(
      (item) => item.price.recurring?.usage_type === 
    )
     (meteredItem) {
       (meteredItem., )
    }
  }
}

---

Customer Portal

// app/api/billing/portal/route.ts
import { NextResponse } from "next/server"
import { stripe } from "@/lib/stripe"
import { getAuthUser } from "@/lib/auth"

export async function POST() {
  const user = await getAuthUser()
  if (!user?.stripeCustomerId) {
    return NextResponse.json({ error: "No billing account" }, { status: 400 })
  }

  const portalSession = await stripe.billingPortal.sessions.create({
    customer: user.stripeCustomerId,
    return_url: `${process.env.NEXT_PUBLIC_APP_URL}/settings/billing`,
  })

  return NextResponse.json({ url: portalSession.url })
}

---

Testing with Stripe CLI

# Install Stripe CLI
brew install stripe/stripe-cli/stripe

# Login
stripe login

# Forward webhooks to local dev
stripe listen --forward-to localhost:3000/api/webhooks/stripe

# Trigger specific events for testing
stripe trigger checkout.session.completed
stripe trigger customer.subscription.updated
stripe trigger invoice.payment_failed

# Test with specific customer
stripe trigger customer.subscription.updated \
  --override subscription:customer=cus_xxx

# View recent events
stripe events list --limit 10

# Test cards
# Success: 4242 4242 4242 4242
# Requires auth: 4000 0025 0000 3155
# Decline: 4000 0000 0000 9995
# Insufficient funds: 4000 0000 0000 9995

---

Feature Gating Helper

// lib/subscription.ts
export function isSubscriptionActive(user: { subscriptionStatus: string | null, stripeCurrentPeriodEnd: Date | null }) {
  if (!user.subscriptionStatus) return false
  if (user.subscriptionStatus === "active" || user.subscriptionStatus === "trialing") return true
  // Grace period: past_due but not yet expired
  if (user.subscriptionStatus === "past_due" && user.stripeCurrentPeriodEnd) {
    return user.stripeCurrentPeriodEnd > new Date()
  }
  return false
}

// Middleware usage
export async function requireActiveSubscription() {
  const user = await getAuthUser()
  if (!isSubscriptionActive(user)) {
    redirect("/billing?reason=subscription_required")
  }
}

---

Common Pitfalls

• Webhook delivery order not guaranteed — always re-fetch from Stripe API, never trust event data alone for DB updates
• Double-processing webhooks — Stripe retries on 500; always use idempotency table
• Trial conversion tracking — store hasHadTrial: true in DB to prevent trial abuse
• Proration surprises — always preview proration before upgrade; show user the amount before confirming
• Customer portal not configured — must enable features in Stripe dashboard under Billing → Customer portal settings
• Missing metadata on checkout — always pass userId in metadata; can't link subscription to user without it