Recover & Grow Subscription Revenue

Track events. We handle the rest. Pre-built workflows recover payments, convert trials, and retain subscribers—optimized across thousands of subscription businesses.

Install the SDK and start recovering revenue in minutes.

1npm install @fourbyfour/sdk

123456import Fourbyfour from '@fourbyfour/sdk'; const fbf = new Fourbyfour({  apiKey: process.env.FOURBYFOUR_API_KEY,  projectId: process.env.FOURBYFOUR_PROJECT_ID});

Get your API key from the dashboard. 12 pre-built workflows optimized for subscription revenue recovery are ready to use.

Two functions. That's all you need.

12345678// Payment failed → triggers recovery workflowawait fbf.track('payment.failed', {  userId: 'cus_9s6XGrhLkFm2pQ',  plan: 'Pro',  amount: 99,  currency: 'USD',  failureReason: 'card_declined'});

1234567// Send context to help optimize deliveryawait fbf.notify({  userId: 'cus_9s6XGrhLkFm2pQ',  timezone: 'America/New_York',  preferredChannel: 'email',  tier: 'premium'});

Answer a few questions about your stack and we'll generate a step-by-step integration guide that you can feed to your AI coding assistant (Claude Code, Cursor, Copilot, etc.).

Two functions. No PII. That's the entire SDK.

1234567891011121314151617181920import Fourbyfour from '@fourbyfour/sdk'; const fbf = new Fourbyfour({  apiKey: process.env.FOURBYFOUR_API_KEY,  projectId: process.env.FOURBYFOUR_PROJECT_ID}); // Minimum: just userId (we use defaults)await fbf.track('payment.failed', {  userId: 'cus_9s6XGrhLkFm2pQ'}); // Full: everything you know (better optimization)await fbf.track('payment.failed', {  userId: 'cus_9s6XGrhLkFm2pQ',  plan: 'Pro',  amount: 99,  currency: 'USD',  failureReason: 'card_declined'});

123456789// Send context anytime to help us optimize deliveryawait fbf.notify({  userId: 'cus_9s6XGrhLkFm2pQ',  timezone: 'America/New_York',  // When to reach them  tier: 'premium',               // Priority signals  preferredChannel: 'email',     // Channel preference  language: 'en',                // Localization  ltv: 1200                      // Value signals});

123await fbf.track('payment.failed', {  userId: 'cus_9s6XGrhLkFm2pQ'});

1234567await fbf.track('payment.failed', {  userId: 'cus_9s6XGrhLkFm2pQ',  plan: 'Pro',  amount: 99,  currency: 'USD',  failureReason: 'card_declined'});

Just-in-time PII. Your data stays in your system until the moment of delivery.

1234567891011POST /api/fourbyfour/resolveHeaders:  x-fbf-signature: sha256=... Body:{  "userId": "cus_9s6XGrhLkFm2pQ",  "fields": ["email", "name"],  "workflowId": "payment-recovery",  "channel": "email"}

123456789101112HTTP 200 OK {  "email": "user@example.com",  "name": "John"} // Or if user not found:HTTP 404 Not Found{  "error": "User not found"}

12345678910111213141516171819202122232425// Express / Next.js API routeapp.post('/api/fourbyfour/resolve', async(req, res) => {  // Verify the request is from Fourbyfour  const signature = req.headers['x-fbf-signature'];  if(!verifySignature(signature, req.body, process.env.FBF_WEBHOOK_SECRET)) {    return res.status(401).json({ error: 'Invalid signature' });  }   const { userId, fields, workflowId, channel } = req.body;   // Fetch user from your database  const user = await db.users.findById(userId);  if(!user) {    return res.status(404).json({ error: 'User not found' });  }   // Return only requested fields  const response: Record<string, string> = {};   if(fields.includes('email')) response.email = user.email;  if(fields.includes('name')) response.name = user.firstName;  if(fields.includes('phone')) response.phone = user.phone;   res.json(response);});

12 subscription revenue workflows. Track the event, we handle timing, channels, and intelligent messaging.

We deliver via the optimal channel. You just provide the resolver endpoint. We handle the rest.