Problem putting sub-pages in the parent-page

Hello everyone!

I am having a strange problem. It isn’t easy to describe, but I’ll do my best.
So, first, I am trying to create a template that writes inside a parent-page some of its sub-pages (or child-page’s) content. Only the sub-page title and its featured image.

This is the code:

<?php
/**
 *	Template Name: Projects
 */
?>

<?php get_header(); ?>

		<div id="primary">
			<div id="content" role="main">

					<?php $subpages = new WP_Query("post_parent=$pageid&post_type='page'&orderby=title&order=DESC");
					if($subpages->have_posts()) : while($subpages->have_posts()) : $subpages->the_post(); ?>
						<div class="post">
							<?php echo '<h3><a href="' . the_permalink() . '">' . get_the_title() . '</a></h3>'; ?>
							<div class="entry">
								<?php echo the_permalink(); ?> <!-- this was not here, it was added to test the permalink, like I'll explain later-->
								<?php the_post_thumbnail( 'single-post-thumbnail' ); ?>
							</div>
						</div>
					<?php endwhile; endif; ?>

			</div><!-- #content -->
		</div><!-- #primary -->

<?php get_footer(); ?>

So, what’s going on, and you’re going to find it really weird, is that this line:

<?php echo '<h3><a href="' . the_permalink() . '">' . get_the_title() . '</a></h3>'; ?>

prints this between the line with the div class post and the div class entry:

<div class="post">
https://cannatafernandes.com/wp/?page_id=23&lang=pt
<h3><a href="">Projecto 1</a></h3>
<div class="entry">

So, not only it does not put the permalink in between the href=”” as it also links to the parent-page (actual page), without any URL inside the href””, don’t know how… But if I take the permalink() of that line it prints well…

Again, all I’m trying to do is to put the title of a subpage linking to its permalink, accompanied with its featured image, inside the parent-page…

Thank you in advance to anyone that tries to solve this… ??