I am trying to add an img in thankyou.php page in my Woocommerce e-shop. I have done the process with moving the file from /plugins/woocommerce/... into a folder /themes/...
Below you can find the code of the thankyou.php file. It is necessary do it this way because I need some order variables to generate the img (totals and number).
<?php
if ( $order ) :
do_action( 'woocommerce_before_thankyou', $order->get_id() );
?>
<?php if ( $order->has_status( 'failed' ) ) : ?>
<p class="woocommerce-notice woocommerce-notice--error woocommerce-thankyou-order-failed"><?php esc_html_e( 'Unfortunately your order cannot be processed as the originating bank/merchant has declined your transaction. Please attempt your purchase again.', 'woocommerce' ); ?></p>
<p class="woocommerce-notice woocommerce-notice--error woocommerce-thankyou-order-failed-actions">
<a href="<?php echo esc_url( $order->get_checkout_payment_url() ); ?>" class="button pay"><?php esc_html_e( 'Pay', 'woocommerce' ); ?></a>
<?php if ( is_user_logged_in() ) : ?>
<a href="<?php echo esc_url( wc_get_page_permalink( 'myaccount' ) ); ?>" class="button pay"><?php esc_html_e( 'My account', 'woocommerce' ); ?></a>
<?php endif; ?>
</p>
<?php else : ?>
<?php wc_get_template( 'checkout/order-received.php', array( 'order' => $order ) ); ?>
<ul class="woocommerce-order-overview woocommerce-thankyou-order-details order_details">
<li class="woocommerce-order-overview__order order">
<?php esc_html_e( 'Order number:', 'woocommerce' ); ?>
<strong><?php echo $order->get_order_number(); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?></strong>
</li>
<li class="woocommerce-order-overview__date date">
<?php esc_html_e( 'Date:', 'woocommerce' ); ?>
<strong><?php echo wc_format_datetime( $order->get_date_created() ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?></strong>
</li>
<?php if ( is_user_logged_in() && $order->get_user_id() === get_current_user_id() && $order->get_billing_email() ) : ?>
<li class="woocommerce-order-overview__email email">
<?php esc_html_e( 'Email:', 'woocommerce' ); ?>
<strong><?php echo $order->get_billing_email(); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?></strong>
</li>
<?php endif; ?>
<li class="woocommerce-order-overview__total total">
<?php esc_html_e( 'Total:', 'woocommerce' ); ?>
<strong><?php echo $order->get_formatted_order_total(); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?></strong>
</li>
<?php if ( $order->get_payment_method_title() ) : ?>
<li class="woocommerce-order-overview__payment-method method">
<?php esc_html_e( 'Payment method:', 'woocommerce' ); ?>
<strong><?php echo wp_kses_post( $order->get_payment_method_title() ); ?></strong>
</li>
<?php endif; ?>
</ul>
<img
class="qrcodecz"
src="https://api.paylibo.com/paylibo/generator/czech/image?accountNumber=2202681982&bankCode=2010&amount=<?php echo $order->get_subtotal(); ?>&currency=CZK&vs=<?php echo $order->get_order_number() ?>&message=svetvramu.cz&size=200"
alt="QR platba"
/>
<?php endif; ?>
<?php do_action( 'woocommerce_thankyou_' . $order->get_payment_method(), $order->get_id() ); ?>
<?php do_action( 'woocommerce_thankyou', $order->get_id() ); ?>
<?php else : ?>
<?php wc_get_template( 'checkout/order-received.php', array( 'order' => false ) ); ?>
<?php endif; ?>
This particular code is what I am trying to generate but it is not working.
<img
class="qrcodecz"
src="https://api.paylibo.com/paylibo/generator/czech/image?accountNumber=2202681982&bankCode=2010&amount=<?php echo $order->get_subtotal(); ?>&currency=CZK&vs=<?php echo $order->get_order_number() ?>&message=svetvramu.cz&size=200"
alt="QR platba"
/>
There is no changes in the thankyou.page (the order totals are still the same). Am I editing the right page? I suppose yes because of the list which is for sure generated from this file.
Thank you for any hint!

You don't need to override checkout/thankyou.php template file. Instead, you can use the following revised code (replacement):
Code goes in functions.php file of your active child theme (or active theme). Tested and works.
On order received (thankyou) page, you will get something like: