Restoring from a read-only encrypted capacity tier

[RubinCompServ]

We are a cloud provider and have a shared VBR for our customers. One customer provided their own Azure Blob and asked us to use it as the Capacity Tier for their backups. We added it as the Capacity Tier and encrypted it with a password. They then mounted the Blob as Read-only on their own VBR and are unable to restore from it. They say that the backups are encrypted (which they are) but there is no way for them to decrypt them. Can a Read-only Blob only be restored from if the backups aren't encrypted?