let formData = new FormData()
            formData.append("event[evidences]", this.hiddenInput.value);
            Rails.ajax({
              url: this.data.get("update-url"),
              type: "PATCH",
              data: formData
              
            });

has_many_attached :evidences

 let formData = new FormData()
            formData.append("event[evidences][]", [this.hiddenInput.value] )
            Rails.ajax({
              url: this.data.get("update-url"),
              type: "PATCH",
              data: formData
              
            });