I do not know the fine print for your d/h's coverage, but I can share our general experience.
Some insurance carriers have a list of covered meds, which are their 'preferred' scripts. For example, someone could be on a stomach med, which we'll call "A" for years. The insurance company wants you to take "B" instead, because it is cheaper. Some will require evidence that you have tried "B" before they will cover "A".
I have found if our doctor writes a note, specifically stating that 'patient is not a candidate for medication "A", and must remain on medication "B", which has been proven successful in this patient', they will cover it.
I would call your doctor's office and ask about their experience with this provider. Good luck.