Thank you for reporting this here. Currently there is a Pega Academy System Issue that can be viewed on the Pega Academy homepage.
Here is what the verbiage says:
Pega Academy System Issue
The Pega Academy team is currently aware of an issue that is impacting learners and blocking access to Pega Academy courses. We are actively working to resolve this issue as soon as possible.
This impacts all users and we apologize in advance for any inconvenience.