All Australians and visitors to Australia have one, regardless of whether they have a Medicare or DVA card or not.
All visitors to Australia have a temporary IHI assigned to them, but they may not realise.
IHI is needed for ePrescribing, if a Provider cannot validate the IHI for a patient, it means the patient has elected to not share this information for electronic record keeping or prescribing.
They will need to contact HI at Services Australia and obtain their IHI to provide the practice themselves.
If they do not wish to supply their IHI they cannot be ePrescribed.