When activating the plugin, an error message was displayed on top of the plugins page:

“The plugin generated 484 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.”

Getting this message:

Checkout
[woocommerce_checkout]

Warning: Cannot modify header information – headers already sent by (output started at /home/theecrea/public_html/wp-content/plugins/woo-awesome-checkout-popup-form/checkout-form.php:1) in /home/theecrea/public_html/wp-content/themes/ronneby/inc/lib/CompileLess/CompileLess.php on line 39

Warning: Cannot modify header information – headers already sent by (output started at /home/theecrea/public_html/wp-content/plugins/woo-awesome-checkout-popup-form/checkout-form.php:1) in /home/theecrea/public_html/wp-admin/includes/misc.php on line 1114

Warning: Cannot modify header information – headers already sent by (output started at /home/theecrea/public_html/wp-content/plugins/woo-awesome-checkout-popup-form/checkout-form.php:1) in /home/theecrea/public_html/wp-includes/pluggable.php on line 1216

Warning: Cannot modify header information – headers already sent by (output started at /home/theecrea/public_html/wp-content/plugins/woo-awesome-checkout-popup-form/checkout-form.php:1) in /home/theecrea/public_html/wp-includes/pluggable.php on line 1216