We are trying to access a WSDL available on an internal test server. When we pro

Have you checked that the URL you're using to access the WSDL is indeed the one that corresponds to the certificate and that the certificate is indeed valid?

Try accessing the WSDL through the browser too to see if you get any warnings about the certificate there too

There is no issue with the WSDL of URl; The site works perfectly fine. When i access the site, IT gives a similar error, BUT gives an option to proceed ahead. So, with browser i have a choice, not when i access using Appian

Below is the exact response i get from IE
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There is a problem with this website's security certificate.

The security certificate presented by this website has expired or is not yet valid.
The security certificate presented by this website was issued for a different website's address.

Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.
We recommend that you close this webpage and do not continue to this website.
1: Click here to close this webpage.
2: Continue to this website (not recommended).

If the browser is giving you the warning too you need to determine why that certificate is invalid, if it's expired then Appian won't be able to consume it. You could try downloading the WSDL and hosting it in a non-https location to be able to use it at design time but that may still fail at runtime, you may want to test this if you cannot have them fix the expired cert.