It produced this output: The requested apache plugin does not appear to be installed
My web server is (include version):
The operating system my web server runs on is (include version): Centos 7, Apache 2.4.6
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): certbot 1.16.0
Package certbot-1.11.0-1.el7.noarch already installed and latest version
Package python2-certbot-apache-1.11.0-1.el7.noarch already installed and latest version
but certbot tells me it is not installed. Please help me how to fix this issue.
That copy of Certbot would have come from installing Certbot using pip install certbot. This is usually not what you want to do; it's not a supported method of installation.
pip will install whatever the latest vesrion published at certbot · PyPI is. Installing it globally is not recommended (for any Python package ever, not just Certbot) because it will conflict with libraries installed via yum.
There is an official and safe way to use pip to install Certbot, and that's using a virtual environment: Certbot - Pip Other.
Yep, that's what the instructions at https://certbot.eff.org/ say to do. With pip it's a bit complicated because there's no precisely clean way to uninstall a set of globally-installed packages once you've installed them, but the commands I suggested a few posts ago should hopefully result in a working installation.