Hi Noel,

I am not sure why you are getting reference key error, could you please try below code.

    public class CreateShippingMethod
    {
        private readonly IMarketService _marketService;

        public CreateShippingMethod(IMarketService marketService)
        {
            _marketService = marketService ?? throw new ArgumentNullException(nameof(marketService));
        }

        public void ConfigureShippingMethods()
        {
            var enabledMarkets = _marketService.GetAllMarkets().Where(x => x.IsEnabled).ToList();

            foreach (var language in enabledMarkets.SelectMany(x => x.Languages).Distinct())
            {
                var languageId = language.TwoLetterISOLanguageName;
                var dto = ShippingManager.GetShippingMethods(languageId);
                var workingDto = (ShippingMethodDto)dto.Copy();

                this.DeleteShippingMethods(workingDto);
                ShippingManager.SaveShipping(workingDto);

                var marketsForCurrentLanguage = enabledMarkets.Where(x => x.Languages.Contains(language)).ToList();
                var shippingSet = this.CreateShippingMethodsForLanguageAndCurrencies(workingDto, marketsForCurrentLanguage, languageId);
                ShippingManager.SaveShipping(workingDto);

                AssociateShippingMethodWithMarkets(workingDto, marketsForCurrentLanguage, shippingSet);
                ShippingManager.SaveShipping(workingDto);
            }
        }

        private void DeleteShippingMethods(ShippingMethodDto dto)
        {
            foreach (var method in dto.ShippingMethod)
            {
                method.Delete();
            }
        }

        private IEnumerable<ShippingMethodDto.ShippingMethodRow> CreateShippingMethodsForLanguageAndCurrencies(ShippingMethodDto dto, IEnumerable<IMarket> markets, string languageId)
        {
            var shippingOption = dto.ShippingOption.First(x => x.Name == "Generic Gateway");
            var shippingMethods = new List<ShippingMethodDto.ShippingMethodRow>();
            var sortOrder = 1;

            //TODO: Add wishing price and currency
            var usdCostExpress = new Money(20, Currency.USD);

            foreach (var currency in markets.SelectMany(m => m.Currencies).Distinct())
            {
                shippingMethods.Add(this.Create(dto, shippingOption, languageId, sortOrder++,
                    "Express-" + currency, $"Express {currency} (1 day)({languageId})", usdCostExpress, currency));

                // TODO: Add more shipping methods.
            }

            return shippingMethods;
        }

        private ShippingMethodDto.ShippingMethodRow Create(ShippingMethodDto dto,
            ShippingMethodDto.ShippingOptionRow shippingOption, string languageId, int sortOrder, string name,
            string description, Money costInUsd, Currency currency)
        {
            Money shippingCost = CurrencyFormatter.ConvertCurrency(costInUsd, currency);
            if (shippingCost.Currency != currency)
            {
                throw new InvalidOperationException("Cannot convert to currency " + currency + " Missing conversion data.");
            }

            return dto.ShippingMethod.AddShippingMethodRow(
                Guid.NewGuid(),
                shippingOption,
                languageId,
                true,
                name,
                "",
                shippingCost.Amount,
                shippingCost.Currency,
                description,
                false,
                sortOrder,
                DateTime.Now,
                DateTime.Now);
        }

        private void AssociateShippingMethodWithMarkets(ShippingMethodDto dto, IEnumerable<IMarket> markets,
            IEnumerable<ShippingMethodDto.ShippingMethodRow> shippingSet)
        {
            foreach (var shippingMethod in shippingSet)
            {
                foreach (var market in markets?.Where(m => m.Currencies.Contains(shippingMethod.Currency)))
                {
                    dto.MarketShippingMethods.AddMarketShippingMethodsRow(market.MarketId.Value, shippingMethod);
                }
            }
        }
    }

Thank you Sanjay,

i actually found code very similar to that here and adapted it too only create a single shipping method with the string i give it (all my shipping methods are 'discovered' during import from another system)

    using EPiServer.ServiceLocation;
    using Mediachase.Commerce;
    using Mediachase.Commerce.Markets;
    using Mediachase.Commerce.Orders.Dto;
    using Mediachase.Commerce.Orders.Managers;
    using Mediachase.Commerce.Shared;
    using System;
    using System.Collections.Generic;
    using System.Linq;

    public class ShippingMethodHelper
    {
        #region singleton

        private static readonly Lazy<ShippingMethodHelper> lazy = new Lazy<ShippingMethodHelper>(() =>
        {            
            return new ShippingMethodHelper();
        });

        public static ShippingMethodHelper Instance => lazy.Value;

        #endregion


        public void ConfigureShippingMethods(string methodName)
        {
            var marketService = ServiceLocator.Current.GetInstance<IMarketService>();
            var enabledMarkets = marketService.GetAllMarkets().Where(x => x.IsEnabled).ToList();
            foreach (var language in enabledMarkets.SelectMany(x => x.Languages).Distinct())
            {
                var languageId = language.TwoLetterISOLanguageName;
                var dto = ShippingManager.GetShippingMethods(languageId);
                var workingDto = (ShippingMethodDto)dto.Copy();
                //DeleteShippingMethods(workingDto);
                //ShippingManager.SaveShipping(workingDto);

                var marketsForCurrentLanguage = enabledMarkets.Where(x => x.Languages.Contains(language)).ToList();
                var shippingSet = CreateShippingMethodForLanguageAndCurrencies(workingDto, marketsForCurrentLanguage, languageId, methodName);
                ShippingManager.SaveShipping(workingDto);

                AssociateShippingMethodWithMarkets(workingDto, marketsForCurrentLanguage, shippingSet);
                ShippingManager.SaveShipping(workingDto);
            }
        }

        private IEnumerable<ShippingMethodDto.ShippingMethodRow> CreateShippingMethodForLanguageAndCurrencies(ShippingMethodDto dto, IEnumerable<IMarket> markets, string languageId, string methodName)
        {
            var shippingOption = dto.ShippingOption.First(x => x.Name == "Generic Gateway");
            var shippingMethods = new List<ShippingMethodDto.ShippingMethodRow>();
            var sortOrder = 1;

            foreach (var currency in markets.SelectMany(m => m.Currencies).Distinct())
            {
                shippingMethods.Add(CreateShippingMethod(dto, shippingOption, languageId, 0, methodName, methodName, new Money(0, Currency.GBP), currency));
            }

            return shippingMethods;
        }

        private ShippingMethodDto.ShippingMethodRow CreateShippingMethod(ShippingMethodDto dto, ShippingMethodDto.ShippingOptionRow shippingOption, string languageId, int sortOrder, string name, string description, Money costInUsd, Currency currency)
        {
            Money shippingCost = CurrencyFormatter.ConvertCurrency(costInUsd, currency);
            if (shippingCost.Currency != currency)
            {
                throw new InvalidOperationException("Cannot convert to currency " + currency + " Missing conversion data.");
            }
            return dto.ShippingMethod.AddShippingMethodRow(
                Guid.NewGuid(),
                shippingOption,
                languageId,
                true,
                name,
                "",
                shippingCost.Amount,
                shippingCost.Currency,
                description,
                false,
                sortOrder,
                DateTime.Now,
                DateTime.Now);
        }

        private void AssociateShippingMethodWithMarkets(ShippingMethodDto dto, IEnumerable<IMarket> markets, IEnumerable<ShippingMethodDto.ShippingMethodRow> shippingSet)
        {
            foreach (var shippingMethod in shippingSet)
            {
                foreach (var market in markets.Where(m => m.Currencies.Contains(shippingMethod.Currency)))
                {
                    dto.MarketShippingMethods.AddMarketShippingMethodsRow(market.MarketId.Value, shippingMethod);
                }
            }
        }