Hi Ben,

All Vendr's APIs return read only entities by default, you need to make it writable to edit it. You can find info on read only and writable entities, and how to make a read only entity writable here https://vendr.net/docs/core/1.8.0/key-concepts/readonly-and-writable-entities/

Ultimately, you'd need something like

using(var uow = _vendrApi.Uow.Create())
{
     var discount = _vendrApi.GetDiscount(discountId).AsWritable(uow)
        .SetActive(false);

    _vendrApi.SaveDiscount(discount);

    uow.Complete();
}

Matt