Install apache2-ssl-dev by entering the following commands in the terminal:
sudo apt update sudo apt install apache2-ssl-dev
Apache HTTP Server (mod_ssl development headers)
The Apache HTTP Server Project's goal is to build a secure, efficient and extensible HTTP server as standards-compliant open source software. The result has long been the number one web server on the Internet. . This package provides the development header and the dependencies for modules that interact with mod_ssl's internal openssl state.