ACME Server can't reach answer file, web browser can

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My domain is:,

I ran this command: letsencrypt.exe --test --san --centralsslstore C:\Central_SSL\

It produced this output:

The ACME server was probably unable to reach

Check in a browser to see if the answer file is being served correctly.

My web server is (include version):IIS 7.5.7600.16385

The operating system my web server runs on is (include version): Windows Server 2088 R2 validates fine, does not. I can reach both answer files with a browser from an external site without any problems. Do I miss anything important here?

Probably! Your browser is using the IPv4 address, while the certificate authority is using the IPv6 address 2001:8d8:87e:7500::41:264b, which you are advertising in DNS via an AAAA record. You should make sure that your web server is set up to serve exactly the same content in IPv4 and IPv6 in exactly the same way.

Notably, this is a difference between and (the former advertises only an IPv4 address, while the latter advertises both addresses).

1 Like

That did the trick, I removed the IPV6 from Thanks a lot for your help!

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