I want to achieve

The following configuration is built with Oracle Cloud.
WAF (SSL communication)
-------public subnet
WebServer (Windows Server 2016)
-------public subnet

As I want to realize, as shown in the figure above, when accessing from the Internet, I want to receive it with WAF and perform HTTPS communication.

I get a 500 Bad Gateway error when I access it in a browser.

What I tried

With the above configuration, when the Web server was verified with CentOS 7.8, HTTPS communication could be performed without problems.

I want you to tell me

The point I would like you to teach the most is that 500 errors can be resolved and HTTPS communication can be done,
In the second point, if there are settings related to SSL and HTTPS communication around IIS settings, please tell me.