When using this API, your level of access depends on the groups you have access to. If your username isn't associated with the group ID (gid or groupId) you selected, then the request fails. You need to use the List Groups operation in version 2 of this API to retrieve groupId values.
To understand groups, you need to understand how accounts work at Akamai. Akamai customers access all their services using an account key. While administrators may have access to more than one account, in general they provision all their web assets under a single account. Customers typically set up groups that correspond to their company's own organizational hierarchy.
You can change group-level information by changing role assignments in the User Admin API, or by either creating or deleting properties in the Property Manager API (PAPI).