Price option not showing up

Dear support,

I have purchased the event calendar pro and Event Tickets but I can’t get the event cost to show up.
Each event appears as free and it can not be modified. While searching on the forums, I found that it was necessary to insert these lines of code in the file “functions.php”:

/* Force the use of the cost field of event and ignore tickets price */
function tribe_just_show_price_field ( $cost, $post_id, $with_currency_symbol ) {

$cost_utils = Tribe__Events__Cost_Utils::instance();
$cost = tribe_get_event_meta( $post_id, ‘_EventCost’ );
if ( $with_currency_symbol ) {
$cost = $cost_utils->maybe_format_with_currency( $cost );
}
return $cost;
}
add_filter( ‘tribe_get_cost’, ‘tribe_just_show_price_field’, 10 , 3 );
/* activate event cost field when using event tickets */
add_filter( ‘tribe_events_admin_show_cost_field’, ‘__return_true’, 100 );

But here is the message I get afterwards:

Warning: Cannot modify header information – headers already sent by (output started at /homepages/5/d558330442/htdocs/clickandbuilds/EcoledeGolfdeLezza/wp-content/themes/kids-club-child/functions.php:15) in /homepages/5/d558330442/htdocs/clickandbuilds/EcoledeGolfdeLezza/wp-admin/includes/misc.php on line 1126

Not having very good knowledge in this area, I’ll admit that there I really do not know what to do to solve the problem ???

I thank you in advance for your help. Regards,
Gabriel