Doctors are different. Some are less cautious than others. Most want to see a patient at least every 3 months when they are on a stimulant. They can certainly charge you for writing the prescription without an office visit.
If the monthly visits are only about him making enough money every month, then it may be time to find another new clinician. The visits should always be about checking in with you regarding medication and mental health.
ADDitude Community Moderator, Parenting ADHD Coach, Podcaster & Author, Mom to teen w/ ADHD, LDs, and autism