Для якоря используй нижний регистр, вот так работает:
* [Server Requirements](#server-requirements)
* [Installation](#installation-in-4-steps)
* [Configuration](#Configuration)
## Server Requirements
---------------------
* PHP >= 7.1.0
* PDO PHP Extension
## Installation in 4 steps
---------------------
Несколько правил:
punctuation marks will be dropped
leading white spaces will be dropped
upper case will be converted to lower
spaces between letters will be converted to -
Источник просторы stackoverflow