ConfigureServiceApiBlock.cs

using Sitecore.Commerce.Core.Commands;
using Sitecore.Commerce.Plugin.Catalog;

namespace Sitecore.Services.Examples.Catalog
{
    using System.Threading.Tasks;

    using Microsoft.AspNetCore.OData.Builder;

    using Commerce.Core;
    using Framework.Conditions;
    using Sitecore.Framework.Pipelines;

    [PipelineDisplayName("ConfigureServiceApiBlock")]
    public class ConfigureServiceApiBlock : PipelineBlock<ODataConventionModelBuilder, ODataConventionModelBuilder, CommercePipelineExecutionContext>
    {
        public override Task<ODataConventionModelBuilder> Run(ODataConventionModelBuilder modelBuilder, CommercePipelineExecutionContext context)
        {
            Condition.Requires(modelBuilder).IsNotNull($"{Name}: The argument cannot be null.");

            var createUpdateSellableItem = modelBuilder.Action("CreateUpdateSellableItem");
            createUpdateSellableItem.Parameter<string>("createUpdateSellableItem");
            createUpdateSellableItem.Returns<bool>();

            return Task.FromResult(modelBuilder);
        }
    }
}