Your customer is using Privilege Cloud Shared Services.

For customers using CyberArk Privilege Cloud Shared Services, the correct format for the CyberArk Vault address is:

vault-<subdomain>.privilegecloud.cyberark.cloud (Option B). This format is used to access the vault services provided by CyberArk in the cloud environment, where <subdomain> is the unique identifier assigned to the customer’s specific instance of the Privilege Cloud.