Explanation:

1. Function Placement: The get_post_comments_count function is placed outside any class definition, making it a global function accessible throughout the plugin’s code.
2. Hook Placement: The add_filter call for add_comment_count_to_post_data is placed outside any functions to ensure it’s executed during the plugin’s initialization.
3. Missing Closing Braces: Double-check for missing closing curly braces (}) in other parts of your code,