This Calculated field is intended to return the string values of a choices field on a content item. Follow instructions here to add the property to your web service. You will need to replace 'Features' with your Property name. https://www.progress.com/documentation/sitefinity-cms/for-developers-custom-calculated-properties

CustomChoicesCalculatedField.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Telerik.Sitefinity.Data;
using Telerik.Sitefinity.DynamicModules.Model;
using Telerik.Sitefinity.Model;
using Telerik.Sitefinity;
using Telerik.Sitefinity.Web.Services.Extensibility;

namespace SitefinityWebApp.Helpers
{
	public class CustomChoicesCalculatedField : CalculatedProperty
	{
		/// <summary>
		/// What type of data is being returned, must be a simple type or something that is already in the service or marked with [DataContract]
		/// </summary>
		public override Type ReturnType
		{
			get
			{
				return typeof(ChoiceOption[]);
			}
		}
		/// <summary>
		/// Returns Choice option for Choices fields on the Jobs Dynamic Module
		/// </summary>
		/// <param name="items">Data beeing returned by the oData service</param>
		/// <param name="manager">Current Manager from the service</param>
		/// <returns></returns>
		public override IDictionary<object, object> GetValues(IEnumerable items, IManager manager)
		{
			var ret = new Dictionary<object, object>();
			foreach (IDataItem item in items)
			{
				var dynamicContent = item as DynamicContent;
				var choices = dynamicContent.GetValue<ChoiceOption[]>("Features");
				if (choices != null)
				{
					ret.Add(item, choices);
				}
			}

			return ret;
		}
	}
}