A First-in-human Study to Assess the Initial Safety, Tolerability, and Effectiveness of the ONSS Bilateral Occipital Nerve Field Stimulation System for the Prophylactic Treatment of Chronic Cluster Headache in Difficult-to-treat Subjects.

The purpose of this clinical trial is to evaluate the safety and effectiveness of the Occipital Nerve Stimulation System (ONSS) in treating chronic cluster headache in adults. The study aims to answer the following questions: * What adverse events or medical complications occur following ONSS implantation and stimulation? * Does treatment with the ONSS reduce the frequency of cluster headache attacks compared with baseline? Participant Involvement Participants will: * Undergo implantation of the ONSS device. * Use the ONSS for a 48-week treatment period. * Attend scheduled clinic visits for follow-up assessments and device evaluations. * Maintain a diary documenting cluster headache attacks and use of rescue medications. * Complete study-related assessments throughout the study period.