Tag manager not working


trying to use google tag manager it requires code in the I tried editing the theme for our website but its returning a white screen see the below code before I add Tag Manager

    echo '<body class="'.implode (' ',get_body_class()).'">'; $  body_top_scripts = get_theme_mod( 'scripts-at-beginning-of-body', '' ); if(trim($  body_top_scripts) <>'') echo $  body_top_scripts; 

after….

    echo '<body <!-- Google Tag Manager (noscript) --> <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=notgonnashowdis" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <!-- End Google Tag Manager (noscript) --> class="'.implode (' ',get_body_class()).'">'; $  body_top_scripts = get_theme_mod( 'scripts-at-beginning-of-body', '' ); if(trim($  body_top_scripts) <>'') echo $  body_top_scripts; 

What can I try? I don’t know what ( 'scripts-at-beginning-of-body', '' ); is tbh but it looks like something I should find.