We are updating the payment method on an Order with this code:

using (var uow = _uowProvider.Create())
{
    var order = _sessionManager.GetOrCreateCurrentOrder(store.Id).AsWritable(uow);

    var store = GetStore();

    // other code remove for brevity    

    var paymentId = _paymentMethodService.GetPaymentMethods(storeId).FirstOrDefault(x => x.PaymentProviderAlias == "total-processing").Id;

    order.SetPaymentMethod(paymentId);

    _orderService.SaveOrder(order);

    uow.Complete();
}

On the _orderService.SaveOrder line, when we look at the order.PaymentInfo.PaymentMethodId property, I can see the Guid of the payment provider.

If I then step past this line and the order is saved, when I then look at the order.PaymentInfo.PaymentMethodId property it is null again.

This is causing us issues when we then retrieve the Order in another controller as the payment provider hasn't been saved.

Any ideas what we're doing wrong?