diff --git a/src/paymentservice/charge.js b/src/paymentservice/charge.js
index 2a16780..aa6c96d 100644
--- a/src/paymentservice/charge.js
+++ b/src/paymentservice/charge.js
@@ -1,4 +1,5 @@
 const cardValidator = require('simple-card-validator');
+const uuid = require('uuid/v4');
 
 class CreditCardError extends Error {
   constructor(message) {
@@ -29,7 +30,7 @@ class ExpiredCreditCard extends CreditCardError {
  * Verifies the credit card number and (pretend) charges the card.
  *
  * @param {*} request
- * @return transaction_id - a random number.
+ * @return transaction_id - a random uuid v4.
  */
 module.exports = function charge(request) {
   const { amount, credit_card: creditCard } = request;
@@ -59,6 +60,6 @@ module.exports = function charge(request) {
   console.log(`Transaction processed: ${cardType} ending ${cardNumber.substr(-4)} \
     Amount: ${amount.currency_code}${amount.amount.decimal}.${amount.amount.fractional}`)
 
-  return { transaction_id: -1 }
+  return { transaction_id: uuid() }
 }
 
diff --git a/src/paymentservice/package-lock.json b/src/paymentservice/package-lock.json
index 6393258..f80804f 100644
--- a/src/paymentservice/package-lock.json
+++ b/src/paymentservice/package-lock.json
@@ -746,6 +746,11 @@
         "ansi-regex": "2.1.1"
       }
     },
+    "uuid": {
+      "version": "3.2.1",
+      "resolved": "https://registry.npmjs.org/uuid/-/uuid-3.2.1.tgz",
+      "integrity": "sha512-jZnMwlb9Iku/O3smGWvZhauCf6cvvpKi4BKRiliS3cxnI+Gz9j5MEpTz2UFuXiKPJocb7gnsLHwiS05ige5BEA=="
+    },
     "window-size": {
       "version": "0.1.4",
       "resolved": "https://registry.npmjs.org/window-size/-/window-size-0.1.4.tgz",
diff --git a/src/paymentservice/package.json b/src/paymentservice/package.json
index ee87b69..f7d8823 100644
--- a/src/paymentservice/package.json
+++ b/src/paymentservice/package.json
@@ -11,6 +11,7 @@
   "dependencies": {
     "@grpc/proto-loader": "^0.1.0",
     "grpc": "^1.12.3",
-    "simple-card-validator": "^1.1.0"
+    "simple-card-validator": "^1.1.0",
+    "uuid": "^3.2.1"
   }
 }