I agree with what Christine said. I'd also add that from the website it looks like Medi-Share uses PHCS as a PPO network.
Does your office have a contractual agreement with PHCS? If so, the claim should have been paid according to your PHCS contractual rates, and you may want to look into whether you are contractually obligated to honor that discount. A PHCS contract could be where the OV reduction is coming from, and that may be something you want to double check before billing the patient for the difference. (Typically, the patient would have needed to present the Medi-Share card showing the PHCS network prior to services being rendered. If that didn't happen, you may not be obligated to honor a PHCS discount.)
If your office is not contracted with PHCS, the member is responsible for anything in excess of what Medi-Share paid.
Info above comes from the Medi-Share Program Guidelines, Section V: Preferred Provider Organization (PPO)
https://www.medishare.com/medi-share-guidelines