Limit EDD Product to 1 purchase

add_filter( 'edd_purchase_download_form','has_already_purchased', 10, 2 );

has_already_purchased($purchase_form, $args){
global $user_ID;
if ( edd_has_user_purchased( $user_ID, $args['download_id'] ) ) {
return ’<p class=”edd_has_purchased”>’ . __( ‘You have already purchased this item, but you may purchase it again.’, ‘edd’ ) . ‘</p>’;

}
}