A Grand Central account is no longer needed to use the Advisor service. The password is not required, and any valid email can be used in the Advisor configuration
CloudBees made the decision in early 2018 to shutter the general availability of the CloudBees Jenkins Advisor program, and move the service to one offered to paid customers. Unfortunately, there didn't appear to be enough interest in the service to continue promoting it for general use. More attention could be given to the service, along with dynamic responses to customers' setups, if it was managed under the umbrella of support. The plugin core functionality didn't change, it simply moved to the internal CloudBees Update Center service. This major version release notes the new restrictions placed on the plugin
If after saving the Advisor configuration you reach a
go.pardot.com url with a message
"Cannot find success page to redirect to. Please use your browser back button." you can just discard it and use your browser back button to come back to your instance (The configuration was correctly saved).