At https://www.mantisbt.org/docs/master/en-US/Admin_Guide/html-desktop/#admin.install.requirements.software

This page has moved: "http://www.php.net/manual/en/installation.php" -> "http://www.php.net/manual/en/install.php"

The automatic redirect failed for me when I clicked the link, showing only a blank page, even when refreshing the page. There did not appear to be any connection problems, and other websites worked fine; also, opening the correct link worked fine. There might have been server-sided issues on php.net causing this to happen, but it could also have been a local issue.

No matter how random this issue was: To easily avoid this from happening in the future, we could update the link instead of relying on the courtesy redirect.