daily-book.php

<?php 

add_filter( 'forminator_custom_form_submit_errors', function( $submit_errors, $form_id, $field_data_array ) {
	if( $form_id != 361 ) {
		return $submit_errors;
	}
	$last_entry = ''; 
	// Change this to the message that you want to show.
	$message = 'Booking has been done for the day. Please book for another day.';
	foreach( $field_data_array as $key => $value ){
		if( $value['name'] == 'date-1' ){
			if( $value['value'] != '' ){
				$last_entry = wpmudev_get_last_entry_by_date( $form_id, $value['value'] );
			}
		}
	}

	if ( ! empty( $last_entry ) ) {
		$submit_errors[]['submit'] = $message;
	}

	return $submit_errors;
},15,3);


add_filter( 'forminator_custom_form_invalid_form_message', 'wpmudev_invalid_form_error', 10, 2 );
function wpmudev_invalid_form_error( $invalid_form_message, $form_id ){
	if( $form_id != 361 ) {
		return $invalid_form_message;
	}

	$last_entry = ''; 
	if( isset( $_POST ) ){
		$date = isset( $_POST['date-1'] ) ?  sanitize_text_field( $_POST['date-1'] ) : '';
		if( $date ){
			$last_entry = wpmudev_get_last_entry_by_date( $form_id, $date );
		}
	}

	if ( ! empty( $last_entry ) ) {
		$invalid_form_message = __( 'Booking has been done for the day. Please book for another day.', 'forminator' );
	}
	
	return $invalid_form_message;
}


function wpmudev_get_last_entry_by_date( $form_id, $date ){
    global $wpdb;
    $table_name       = Forminator_Database_Tables::get_table_name( Forminator_Database_Tables::FORM_ENTRY_META );
    $entry_table_name = Forminator_Database_Tables::get_table_name( Forminator_Database_Tables::FORM_ENTRY );
    $sql              = "SELECT m.`entry_id` FROM {$table_name} m LEFT JOIN {$entry_table_name} e ON(e.`entry_id` = m.`entry_id`) WHERE e.`form_id` = %d AND m.`meta_key` = %s AND m.`meta_value` = %s order by m.`meta_id`";
    $entry_id         = $wpdb->get_var( $wpdb->prepare( $sql, $form_id, 'date-1', $date ) );
    if ( $entry_id ) {
        return $entry_id;
    }
    return false;
}