I am using moodle sandbox for LTI 1.3 integartion with my tool. I was able to connect with the tool from the moodle platform. All of a sudden it is throwing me an error.
I'd suggest trying to set this up using HTTPS URLs. I.e. https://ltiadvantagevalidator.imsglobal.org/. It looks like you've got an HTTP in there somewhere, but it's hard to say given the limited information.
My only guess would be that the validator site's session has expired. Looking at that first error, it seems to suggest that you're seeing an error page on the validator. Like I said, that's just a guess though. unfortunately, there's not much else I can suggest. Maybe others who have used that tool with the demo site can provide more insight.