Most online prescriptions do require a video consultation to make sure you get a proper check up, so the doctor can choose the appropriate treatment for your condition. Sometimes a phone call may be adequate. The AHPRA Medical Board, which sets standards for doctors, has made this very clear in its updated telehealth guidelines
Occasionally, if a doctor is caring for a patient who they know very well, it may be appropriate to prescribe treatment following text messages/email, but this is very much an exception.