BuddyPress.org

Use WP to get the id: get_current_user_id();

Or avoid calling the bp global and use bp_loggedin_user_id()

I’m not sure what exactly is on line 8 but make sure you use opening and closing PHP tags like this:

<?php bp_loggedin_user_id(); ?>

<?php get_current_user_id(); ?>

Sorry, I didn’t see you’d posted the link to your code. I don’t think the 500 Internal Server Error is being caused by your use of those functions. Perhaps the error you’re getting is a result of code elsewhere?

get_current_user_id() returns an int. Not sure if the type in this case will make much difference but perhaps your function is expecting a string?

Try doing this:

$user_id = get_current_user_id();
$user_id = (string)$user_id;

Ref: https://codex.wordpress.org/Function_Reference/get_current_user_id

To explain what I mean’t, see this example:

http://codepad.org/kY1hW06z