ERROR after checkout = "Warning: Cannot modify header information....."

[cylis]

While testing the Demo / Test Mode in WP 5.5 we go this error after Checkout:

Warning: Cannot modify header information - headers already sent by (output started at /home/username/public_html/wp-content/plugins/2c2p-redirect-api-for-woocommerce/Includes/wc-2c2p-setting.php:1) in /home/username/public_html/wp-includes/pluggable.php on line 1296

We noticed in the 2c2p-redirect-api-for-woocommerce/Includes/wc-2c2p-setting.php file there was an empty space before the <?php code in line 1.

After removing that empty space, it was fine.