<?php
if(empty($payment_info)){
$content .= 'You have now booked this room. You have to pay for the room upon arrival day ';
}
?>
one small correction to the code. The TEXT_DOMAIN needed two “” wrapped around it, so the code looks like this:
<?php
$content .= __('You have now booked this room. You have to pay for the room upon arrival day', "gdlr-hotel");
?>