How to highlight

I'm trying to figure out how to get a highlight to show in 4coder. Eventually I want to be able to implement something equivalent to vim's visual mode but to start I'm just trying to figure out how to get a simple highlight showing. Here is my current attempt:

CUSTOM_COMMAND_SIG(highlight)
{
    View_Summary view = get_active_view(app, AccessProtected);

    int32_t pos1 = view.cursor.pos;

    move_right(app);
    move_right(app);
    move_right(app);
    move_right(app);
    move_right(app);
    move_right(app);
    move_right(app);
    refresh_view(app, &view);

    int32_t pos2 = view.cursor.pos;

    view_set_highlight(app, &view, pos1, pos2, true);
};

As I understand it, all space from pos1 to pos2 should be highlighted, but it is not highlighting. What am I missing?