Array as Public Property; Need to Set Value at Index

    public class GetCapabilitiesRequest
    {
        [MessageBodyMember(Namespace = "http://www.onvif.org/ver10/device/wsdl", Order = 0)]
        [XmlElement("Category")]
        public CapabilityCategory[] Category;

        public GetCapabilitiesRequest();
        public GetCapabilitiesRequest(CapabilityCategory[] Category);
    }

public enum CapabilityCategory
{
  All = 0,
  Analytics = 1,
  Device = 2,
  Events = 3,
  Imaging = 4,
  Media = 5,
  PTZ = 6
}

GetCapabilitiesRequest caps = new() {
  Category[0] = CapabilityCategory.All
}

Cannot initialize type 'GetCapabilitiesRequest' with a collection initializer because it does not implement 'System.Collections.IEnumerable' [proj_name]
The name 'Category' does not exist in the current context [proj_name]
Invalid initializer member declarator [proj_name]