When trying to create a namespace at path, it returns the following error.
$ vault namespace create ns1
Error creating namespace: Error making API request.
URL: PUT http://127.0.0.1:8200/v1/sys/namespaces/ns1
Code: 404. Errors:
* 1 error occurred:
* unsupported path
Creating new secret engines and putting new kv entries are working well.
It worked with the Vault Enterprise version.
The namespace support is only available with Vault Enterprise.