Hi Darko,
Can you please run the below query alone [without python]from your Ops center server and check whether all existing volumes of your storage system is getting listed or not?
GET https://ipAddress/v1/storage-systems/storageSystemId/volumes
Because, the above query should display all the volumes of a storage system. Please let us know. The below query should also give you a summary of all volumes along with the volume number, would be great if you can also check it.
GET https://ipAddress/v1/storage-systems/storageSystemId/volumes/summary
Regards
Prasenjit