Following AEP Provisioning

Setting up access

Once AEP has been provisioned, even if you are the named administrator, you must give yourself and your team access to AEP resources via the admin console. If not, when you attempt to open Platform, you’ll be told that you haven’t been given permission to any sandboxes. When opening the console, select the proper organization and ID under which the new environment was provisioned.

To configure access control for Experience Platform, you must have system or product administrator privileges for an organization with an Experience Platform product. The minimum role that can grant or withdraw permissions is a product administrator. Other administrator roles that can manage permissions are system administrators (no restrictions). See the Adobe Help Center article on administrative roles for more information.

https://experienceleague.adobe.com/docs/experience-platform/access-control/home.html?lang=en#adobe-admin-console

To kick start the project, ensure you’ve added your users to the Default production all access and Sandbox Administrators rolls. This will provide full access to the environment and the ability to see and create additional sandboxes.