Add BuddyDrive editor to the BuddyPress compose private message screen, the button will appear over the submit one

bp-custom.php

<?php

function test_bp_message_compose() {
    // Always check the editor is available to prevent fatals!
    if ( bp_is_my_profile() && function_exists( 'buddydrive_editor' ) ) {
        // 'message_content' is the id attribute of the textarea to send private messages
        buddydrive_editor( 'message_content' );
    }
}
add_action( 'bp_after_messages_compose_content', 'test_bp_message_compose' );