There's a fix to support multi tenancy planned for TP12, see https://github.com/3scale/3scale-istio-adapter/issues/102

However, in TP11 in order to support multi tenancy, it is necessary to change the name of the namespace.
e.g. if your tenant has the adapter in the namespace 'tenant-foobar-istio-system'
you need to change 'istio-system' for 'tenant-foobar-istio-system' in the namespace field of the templates generated by the adapter's cli