A2 Hosting Let's Encrypt Can't Install Certificate on ASP.NET Core Application

I have an ASP.NET Core app hosted by A2 Hosting. A2 Hosting provides free SSL certificate through Let's Encrypt, so I decided to install it for my application.

Problem

Since the portal is by Plesk, I follow the guide in:

https://support.plesk.com/hc/en-us/articles/115000165013

However, it didn't work as expected.

Solution

My application still has a web.config file. After trying different ways, I commented out aspNetCore module in the web.config and then the certificate was installed successfully. By commenting the module, ASP.NET Core processing by IIS is disabled, so the validation request by Let's Encrypt is treated like a regular request towards a static file.