We have a customer (a restaurant) who needs to pay for items not currently in stock/available in our online store. When they try to pay via the invoice link I sent with their draft order they get an error. I don't want to make those items live for the general public. How can I accept online payments for things I'm not selling in the regular store?
If you use the "Reserve Items" function in the draft order screen when setting up the order, it should allow the customer to complete checkout as long as they complete it within the amount of time you set the reserve for.
You can leave the inventory quantity at 0 before they checkout. However, once they do checkout, it will set your inventory quantities to a negative quantity of whatever the amount they purchased. Afterwards, you can reset it back to 0, or leave it negative and when you transfer your inventory in, it will just subtract automatically.