If the user wishes to consider the username instead of the nicename when clicking on the message button on the user profile, you may follow the below guideline

Note: Make sure to have a complete site backup before proceeding

    1. Go to Appearance - Theme Editor.

    2. Under Select theme to edit, choose (BuddyBoss Child/whatever theme is active), then click Select.

    3. Below Theme Files, select Theme Functions (functions.php).

    4. Append the code just before the closing PHP tag “?>”:

function bb_override_button_message() {
return apply_filters( 'bp_get_send_private_message_link', wp_nonce_url( bp_loggedin_user_domain() . bp_get_messages_slug() . '/compose/?r=' . bp_core_get_username( bp_displayed_user_id() ) ) );

}
add_filter('bp_get_send_private_message_link','bb_override_button_message');

    5. Click Update File to save the changes.

Note: Any modifications are considered as custom work already. Know more about our Support Policy here: https://www.buddyboss.com/support-policy/