Is it possible to handle two or more shortcodes in a single page?

From the PHP Manual on require_once:

The require_once statement is identical to require except PHP will check if the file has already been included, and if so, not include (require) it again.

The second time your shortcode handler is run, the view/template will not be executed.
Hence no output.

Change
require_once "/front_end/view/api-list.php";
to
require "/front_end/view/api-list.php";
and you ought to be fine.

error code: 523