diff --git a/src/index.html b/src/index.html
index 54fa640..2ebadd0 100644
--- a/src/index.html
+++ b/src/index.html
@@ -23,7 +23,7 @@
     <section>
         <h1>API</h1>
         <h4 id="api-qrcode"><a href="#api-qrcode">&#128279;</a> <code>GET /api/qrcode</code></h4>
-        <p>Following the specification from official documentation - <a href="https://www.upn-qr.si/uploads/files/NavodilaZaProgramerjeUPNQR.pdf">NavodilaZaProgramerjeUPNQR.pdf</a>, section 4. - "Vsebina kode QR"</p>
+        <p>Following the specification from official documentation - <a href="https://www.upn-qr.si/uploads/files/NavodilaZaProgramerjeUPNQR.pdf">NavodilaZaProgramerjeUPNQR.pdf</a>, section <code>4. Vsebina kode QR</code>.</p>
         <br>
 
         <div>
@@ -51,9 +51,9 @@
             
             <h5 id="api-qrcode-amount"><a href="#api-qrcode-amount">&#128279;</a> <code>amount</code></h5>
             <div>
-                Regex: <code>^(?=.{11}$)[0]{1,11}[1-9]{0,11}$</code>
+                Regex: <code>^(?=.{11}$)[0]{1,11}[0-9]{0,11}$</code>
                 <br>
-                Demo: <a href="https://regex101.com/r/kbIqwu/1">regex101.com/r/kbIqwu/1</a>
+                Demo: <a href="https://regex101.com/r/Tyq5S1/1">regex101.com/r/Tyq5S1/1</a>
             </div>
             
             <h5 id="api-qrcode-purpose_code"><a href="#api-qrcode-purpose_code">&#128279;</a> <code>purpose_code</code></h5>
diff --git a/src/index.js b/src/index.js
index 215d95b..906daf5 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,13 +1,108 @@
 import express from 'express'
 import path from 'path'
+import qrcode from 'qrcode'
+import cors from 'cors'
 import { dirname } from 'path'
 import { fileURLToPath } from 'url'
 
 const app = express()
 const __dirname = dirname(fileURLToPath(import.meta.url))
 
+app.use(cors())
+
+app.get('/api/qrcode', async (req, res) => {
+    const errors = []
+
+    if (!req.query.client_name) errors.push("client_name is required")
+    if (!String(req.query.client_name).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("client_name does not match the required format")
+    }
+    if (!req.query.client_address) errors.push("client_address is required")
+    if (!String(req.query.client_address).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("client_address does not match the required format")
+    }
+    if (!req.query.client_city) errors.push("client_city is required")
+    if (!String(req.query.client_city).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("client_city does not match the required format")
+    }
+    if (!req.query.amount) errors.push("amount is required")
+    if (!String(req.query.amount).match(/^(?=.{11}$)[0]{1,11}[0-9]{0,11}$/)) {
+        errors.push("amount does not match the required format")
+    }
+
+    // SET DEFAULT PURPOSE_CODE
+    if (!req.query.purpose_code) req.query.purpose_code = "OTHR"
+    if (!String(req.query.purpose_code).match(/^[A-Z]{4}$/)) {
+        errors.push("purpose_code does not match the required format")
+    }
+
+    if (!req.query.payment_purpose) errors.push("payment_purpose is required")
+    if (!String(req.query.payment_purpose).match(/^[A-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,40}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("payment_purpose does not match the required format")
+    }
+
+    if (!req.query.iban) errors.push("iban is required")
+    if (!String(req.query.iban).match(/^[A-Z]{2}\d{17}$/)) {
+        errors.push("iban does not match the required format")
+    }
+
+    if (!req.query.reference) errors.push("reference is required")
+    if (!String(req.query.reference).match(/^[A-Z]{2}[0-9\-]{1,24}$/)) {
+        errors.push("reference does not match the required format")
+    }
+
+    if (!req.query.issuer_name) errors.push("issuer_name is required")
+    if (!String(req.query.issuer_name).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("issuer_name does not match the required format")
+    }
+    if (!req.query.issuer_address) errors.push("issuer_address is required")
+    if (!String(req.query.issuer_address).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("issuer_address does not match the required format")
+    }
+    if (!req.query.issuer_city) errors.push("issuer_city is required")
+    if (!String(req.query.issuer_city).match(/^[a-zA-Z0-9ČŠŽĐ](?:[A-Z0-9 ČŠŽĐ]{0,31}[A-Z0-9ČŠŽĐ])?$/i)) {
+        errors.push("issuer_city does not match the required format")
+    }
+
+    if (errors.length > 0) return res.status(400).send({
+        ok: false,
+        errors
+    })
+
+    let text = `UPNQR
+
+
+
+
+${req.query.client_name}
+${req.query.client_address}
+${req.query.client_city}
+${req.query.amount}
+
+
+${req.query.purpose_code}
+${req.query.payment_purpose}
+
+${req.query.iban}
+${req.query.reference}
+${req.query.issuer_name}
+${req.query.issuer_address}
+${req.query.issuer_city}`
+
+    text = `${text}\n${text.length + 1}`
+
+    const code = await qrcode.toDataURL(text, { errorCorrectionLevel: 'H' })
+
+    var img = new Buffer.from(code.split(',')[1], 'base64')
+    res.writeHead(200, {
+      'Content-Type': 'image/png',
+      'Content-Length': img.length 
+    })
+    res.end(img)
+
+})
 
 app.get('/', (req, res) => res.sendFile(path.join(__dirname, 'index.html')))
 app.get('/style.css', (req, res) => res.sendFile(path.join(__dirname, 'style.css')))
 
-app.listen(80, () => console.log(`UPN-QR started on port 80`))
\ No newline at end of file
+app.listen(process.env.PORT || 80, () => console.log(`UPN-QR started on port ${process.env.PORT || 80}`))
\ No newline at end of file