PHP: Echo not working

In the profile.php-file, the users profile data should be displayed. The previous .html-version of this version worked, but since i need to access the session variables set on login, i changed it to a php file.

The profile.php gets called automatically from the loginuser.php and is executed. I tested this with ordinary html elements, outside of the <?php ?> tag.

    <div id="page-wrapper" class="wrapper">
        <button> test </button>
                echo '<p> Testing, but not working </p>';
                echo 'not set';

UPDATE: Yes after few hours of searching, I finally realised the error. Ofc it needs to be $_SESSION[] instead of $_SESSION(). Feel free to delete this.