add server url

.env.example

@@ -1,3 +1,4 @@
 STATIC_DIR='./client'
 PAYSTACK_SECRET_KEY=
 PORT='5000'
+SERVER_URL='http://localhost:5000'

README.md

@@ -26,10 +26,11 @@ git clone https://github.com/PaystackOSS/sample-subscriptions-app
 npm install
 ```
 
-3. Rename the `.env.example` file to `.env` and add your Paystack secret key. You can also change the default port from 5000 to a port of your choosing:
+3. Rename the `.env.example` file to `.env` and add your Paystack secret key, and your server's URL including the port. This is necessary for the callback URL you'll be redirected to after completing a transaction. You can also change the default port from 5000 to a port of your choosing:
 
 ```
 PAYSTACK_SECRET_KEY=sk_domain_xxxxxx
+SERVER_URL=http://localhost:5000
 ```
 
 4. Start the application

server.js

@@ -81,7 +81,7 @@ app.post('/initialize-transaction-with-plan', async (req, res) => {
       amount,
       plan,
       channels: ['card'], // limiting the checkout to show card, as it's the only channel that subscriptions are currently available through
-      callback_url: 'http://localhost:5000/account.html',
+      callback_url: `${process.env.SERVER_URL}/account.html`,
     });
 
     if (initializeTransactionResponse.status === false) {