Partial decline for PMB

Reference No MH***. I have a son who is disabled. Every year we complete PBM application form for his annual claims depending on the need and recommendation from the Physiothe****** and Occupational The******. This year we got a recommendation for Orthotics. A motivation was done by the Orthopedic and submitted to GEMS. Last week we received feedback for the claim, only 20% of the claim will be paid to GEMS. From what I understand a PBM program is a gap cover for claims that are outside of the normal cover for people with special needs, in this instance a child who is paraplegic. Can someone please clarify the decline and way forward. My child needs the devices in order to progress in his therapy.