Solution:
Note that there’s an IF and an ENDIF which need to be wrapped around the ACF fields.
Also note that the default WP the_content() code must remain in place — even if you’re not using it for content in your template.
<div class="entry-content clearfix">
<!-- HIDES ACF FIELDS for use with WP password protect feature -->
<?php if( !post_password_required( $post )): ?>
<h2><?php the_field( 'business_name' ); ?></h2>
<p><?php the_field( 'client_name' ); ?></p>
<p><small><?php the_field( 'date' ); ?></small></p>
<h1><?php the_field( 'introduction_title' ); ?></h1>
<p><?php the_field( 'introduction_text' ); ?></p>
<!-- ENDS HIDE ACF FIELDS with WP Password Protect -->
<?php endif; ?>
<?php the_content(); ?>
</div><!-- .entry-content -->
