Custom html in sidebar unable to add script

Question

In Layout, when I tick the option to add custom html to everypage sidebar with the following contents

<script type="text/javascript">(function() {var script=document.createElement("script");script.type="text/javascript";script.async =true;script.src="https://telegram.im/widget-button/index.php?id=@vafak";document.getElementsByTagName("head")[0].appendChild(script);})();</script>
<a href="https://telegram.im/@vafak" target="_blank" class="telegramim_button telegramim_shadow telegramim_pulse" style="font-size:26px;width:48px;background:#27A5E7;box-shadow:1px 1px 5px #27A5E7;color:#FFFFFF;border-radius:50px;" title=""><i></i></a>

I can not save it. Whenever, I click on save options, it takes me to the main page.