if even a txt or html results into error 404 i would make 100% sure the bindings, IP address, and DNS is set 100% correct (in general it means it points to a different site or server).

Alternative reasons can be permission issues, or removing the mime types (manually as by default html, txt , etc is always supported)

Thank you Marco. I checked the bindings, all seems ok, ip address and dns are also okay, when visiting .com externally it points to my server, and the default "IIS Windows Server Welcome" page shows up.

I'll go ahead and dig into permission issues and mime types and report back 🙂 Thank yoU!

Just to make sure: .com isn't the site your trying the html / txt's / php on then right?
as the Default IIS welcome page means the server has no bindings for it to a specific site, which makes it hit the "Default website" site in IIS (basically any url pointing to the IP address without any binding to another site)

Yeah not sure why the forum removed the domain place holder I had.

The domain itself is (arsenic.design)

I added this domain via SolidCP and it's listed in IIS under "sites"

hmm alright.
arsenic.design also points to default IIS page for me externally.
Can you make sure iis has a binding for it on the arsenic.design site in iis? (using iis management)

So I went into the site bindings.

And everything seemed fine.

www.arsenic.design -> public server ip
arsenic.design -> public server ip

However when I changed the binding to
www.arsenic.design -> private server ip
arsenic.design -> private server ip

It works! Awesome.

However, why does this work? But not when my servers public ip is used? Was I wrong all along shouldnt have put the public ip?

Glad you figured it out 🙂
From the sound of it your server is behind a NAT firewall, this means the Firewall translates the External IP to an Internal ip (and your end destination only sees the Internal ip)

in such cases you will always need to use internal ip or wildcard * (any ip)