Hi backinstereo,
Contoso Ltd is a fictional company used for sample data.
Did you open subscription center directly?
If so, to test such type of marketing page, we should run a simple customer journey to send marketing email to test contact, because SC only works when it is opened via the link of marketing email.
Please refer to following troubleshooting steps:
1. Open Default Marketing Page(subscription center) record, check whether its Full page URL is valid.
(We will see error message if we open the form/page directly.)
2. Open Default Content Settings record, check whether URL of the default marketing page is inserted to Subscription center field.

3. Check whether content settings with valid subscription center link is applied to content settings field of customer journey.

4. Set up a customer journey to test.
Regards,
Clofly