A Study of Andecaliximab in Participants With Fibrodysplasia Ossificans Progressiva (FOP)

This study is researching an experimental drug called andecaliximab. The study will include pediatric and adult patients with fibrodysplasia ossificans progressiva (FOP). The study will evaluate how safe and effective andecaliximab is in patients with FOP. The study is looking at several research questions, including: * Safety of andecaliximab in participants with FOP * Whether andecaliximab reduces the number of new heterotopic bone lesions (Heterotopic Ossification; HO) * Whether andecaliximab reduces the number or severity of flare-ups * Pharmacokinetics/pharmacodynamics (PK/PD): How much study drug is in your blood at different times and its impact on blood biomarker(s) * Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)