Verify Paystack Payments in Firebase Cloud Functions

// functions/src/index.ts
import { onRequest } from "firebase-functions/v2/https";
import { defineSecret } from "firebase-functions/params";
import { getFirestore } from "firebase-admin/firestore";
import { initializeApp } from "firebase-admin/app";
import * as cors from "cors";

initializeApp();

const paystackSecretKey = defineSecret("PAYSTACK_SECRET_KEY");
const corsHandler = cors({ origin: true });

export const verifyPayment = onRequest(
  { secrets: [paystackSecretKey] },
  async (req, res) => {
    corsHandler(req, res, async () => {
      const reference = req.query.reference as string || req.body?.reference;

      if (!reference) {
        res.status(400).json({ error: "Reference is required" });
        return;
      }

      const secretKey = paystackSecretKey.value();

      try {
        const paystackRes = await fetch(
          "https://api.paystack.co/transaction/verify/" + encodeURIComponent(reference),
          {
            headers: { Authorization: "Bearer " + secretKey },
          }
        );

        const paystackData = await paystackRes.json();

        if (!paystackData.status || paystackData.data.status !== "success") {
          res.status(400).json({
            verified: false,
            status: paystackData.data?.status,
            message: paystackData.data?.gateway_response || "Payment not verified",
          });
          return;
        }

        const txData = paystackData.data;
        const db = getFirestore();

        // Check idempotency
        const orderRef = db.collection("orders").doc(reference);
        const order = await orderRef.get();

        if (order.exists && order.data()?.status === "paid") {
          res.json({
            verified: true,
            amount: txData.amount / 100,
            currency: txData.currency,
            reference: txData.reference,
            already_processed: true,
          });
          return;
        }

        // Update Firestore
        await orderRef.set({
          status: "paid",
          paid_at: new Date().toISOString(),
          amount_paid: txData.amount / 100,
          currency: txData.currency,
          customer_email: txData.customer.email,
        }, { merge: true });

        res.json({
          verified: true,
          amount: txData.amount / 100,
          currency: txData.currency,
          reference: txData.reference,
          customer_email: txData.customer.email,
        });
      } catch (error) {
        res.status(500).json({ error: "Verification failed" });
      }
    });
  }
);

// After Paystack checkout redirect
async function verifyPayment(reference: string) {
  var response = await fetch(
    "https://<region>-<project-id>.cloudfunctions.net/verifyPayment?reference=" + reference
  )

  var result = await response.json()

  if (result.verified) {
    // Grant access, show success screen
    console.log("Payment confirmed:", result.amount, result.currency)
  } else {
    // Show failure or retry
    console.error("Verification failed:", result.message)
  }
}

This guide is part of the Paystack integration guides by language and framework series.

Next: Handle Paystack Webhooks in Firebase Cloud Functions

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