Can't access http://www.wiley.com/go/sybextestprep for online practice test for AWS Solution Architect Associate exam.
AWS Certified Solutions Architect official study guide points to the above link for taking practice tests.
I'm sorry to hear you're having issues, are you seeing an error message of any sort? To clarify here are the steps to retrieving your PIN:
2. Select ' Click here to register
3. Select your product from the drop down
4. Fill in your contact information and provide the answer to the challenge question
6. When you receive the email with the PIN, follow the link within the email or find your book from this page and use the Register PIN or Login link to register for access
Please let me know if you have any other questions.