Hi,
I have the same issue with this plugin.
The problem is certbot-auto script is very old in this plugin: v0.26.1
Code
- DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
I've replaced this script to the latest version and the installation ran successfully without error.
After that you can run "force retry" command on i-MSCP admin page.