I am learning XSS for ethical purposes and I cannot seem to figure this one out on my own. I am trying to use XSS (legally) on a site by appending a <script> at the end of the URL. This results in a message saying Error 404: The page //www.###.com/###/\<script>alert('XSS')\</script> was not found.. The code in chrome dev tools looks like

<div class="text">
    <p>
        "Error 404: The page https://www.###.com/###/<script>alert('XSS')</script> was not found."
    </p>

When editing as HTML:

Error 404: The page https://www.redditinc.com/press/<script>alert('XSS')</script> was not found.

When I try to break out using ", I get the following:

dev tools:

<div class="text">
    <p>
        "Error 404: The page https://www.###.com/###/"<script>alert('XSS')</script> was not found."
    </p>

HTML:

Error 404: The page https://www.redditinc.com/press/"&lt;script&gt;alert('XSS')&lt;/script&gt; was not found.

Same thing goes for '. I'm new to penetration testing, and XSS. Is there anything I can do?