Author Links Display Twice

I’m using this code to create a shortcode:

// Adds [coauthor_byline] shortcode
add_shortcode( 'coauthor_byline', 'coauthor_byline' );

function coauthor_byline()  {
	if ( function_exists( 'coauthors_posts_links' ) ) { ?>
<style>
	.co-byline,
	.co-byline a {
		font-size:14px;
		font-weight:normal;
		color:#999999!important;
		text-transform:uppercase;
		font-family:'Blair ITC',sans-serif;
		transition: all 0.2s;
	}
	.co-byline a:hover {
		color: #800000!important;
		transition: all 0.2s;
	}
	</style>
		<h2 class="co-byline">By <?php echo coauthors_posts_links(); ?></h2>
		<?php
	}
}

And it prints the names twice: https://i.imgur.com/Anpk0wk.png