In umbraco v7 we make use of ApplicationContext which throws an error when upgrading to v8 , and also when we make us of IScope we get an error on getting the cache.

 public abstract class ApiServiceBase
    {
        protected readonly Uri baseUrl;
        protected readonly ApplicationContext appContext;
        protected readonly UmbracoContext umbContext;
        protected readonly IRuntimeCacheProvider cache;
        protected readonly IPublishedContent tradeRoot;
        protected readonly IPublishedContent publicRoot;

        public ApiServiceBase(ApplicationContext appContext, UmbracoContext umbContext)
        {
            ApplicationContext applicationContext = appContext;
            if (applicationContext == null)
                throw new ArgumentNullException(nameof(appContext));
            this.appContext = applicationContext;
            UmbracoContext umbracoContext = umbContext;
            if (umbracoContext == null)
                throw new ArgumentNullException(nameof(umbContext));
            this.umbContext = umbracoContext;
            this.cache = appContext.ApplicationCache.RuntimeCache;
            this.baseUrl = WebAPI.Helpers.UriHelper.GetBaseUriForSite(umbContext.HttpContext);
            this.tradeRoot = this.cache.GetUmbracoCacheItem<IPublishedContent>("ApiCache.TradeRoot", (Func<IPublishedContent>)(() => umbContext.ContentCache.GetAtRoot().FirstOrDefault<IPublishedContent>((Func<IPublishedContent, bool>)(c => c.ContentType.Alias == "Home"))), 240);

        }
    }

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

public EventsResponse GetAll()
        {
            LogHelper.Info<EventsController>(string.Format("Web API request to {0} via {1}", Request.RequestUri, Request?.Headers.UserAgent));
            EventsResponse eventsResponse = new EventsResponse();
            EventsService eventsService = new EventsService(this.ApplicationContext, this.UmbracoContext);

            try
            {
                eventsResponse.events = eventsService.GetAllevents();
                eventsResponse.Success = true;
            }
            catch (Exception ex)
            {
                LogHelper.Info<EventsController>(string.Format("API Error calling events GetAll - {0}", ex.ToString()));
                eventsResponse.Error = ex.Message;
            }

            return eventsResponse;
        }