By default, WP doesn’t allow content to be added to the posts page.
What you can do is use GP Hooks to target the posts page, and add your content that way.
For exmaple, in GP Hooks, add this to the “Before Content” hook:
<?php if ( is_home() ) : ?> Everything in here will show up on the posts page <?php endif; ?>
Let me know if that works for what you’re trying to do 🙂