PHP QR Code outputting .png as a character string - php

Question

I've built my first WordPress plugin to create a QR Code from a form.
It's just for learning purposes and would not meet standards for commercial release.
However it works perfectly on my local server in WAMP using Twenty Twenty theme.
When i test it on my live site (with a commercial theme) the qr code in .png format is displayed as a atring of characters similar to this.
�PNG IHDR{{n m<�PLTE���U��~ pHYs���+aIDATH���1�� ��P��H�W�]���� �΂0;>_�n�ζ�X����w����h�
The string is much longer, but i just put a snippet in to show what i mean.
Below is my plugin code and it includes the full untouched phpqrcode library.
<?php
/*
* Plugin Name: QR Code Generator
* Plugin URI: https://www.example.com/qr-code-generator
* Description: A plugin that allows you to easily generate QR codes for use on your website.
* Version: 1.0
* Author: Your Name
* Author URI: https://www.example.com
* License: GPL2
*/
include_once( plugin_dir_path( __FILE__ ) . 'phpqrcode/qrlib.php' );
function qr_code_shortcode( $atts ) {
// Extract the attributes
extract( shortcode_atts( array(
'text' => '',
), $atts ) );
global $post;
// Check if the shortcode is present in the post or page
if ( has_shortcode( $post->post_content, 'qr_code' ) ) {
// Check if the form has been submitted
if ( isset( $_POST['qr_code_text'] ) ) {
$text = sanitize_text_field( $_POST['qr_code_text'] );
// Generate the QR code
QRcode::png( $text );
} else {
// Display the form
ob_start();
echo '<form method="post">';
echo '<label for="qr_code_text">Enter the text for the QR code:</label><br>';
echo '<input type="text" name="qr_code_text" id="qr_code_text"><br>';
echo '<input type="submit" value="Generate QR Code">';
echo '</form>';
return ob_get_clean();
}
}
}
add_shortcode( 'qr_code', 'qr_code_shortcode' );
Any suggestions as to why it would work in one site and not on another ?
I've tried using base64 on the image thinking it was that but to no avail.