Buyer wants me to pay for return shipping. I made a mistake.

[surplus_discounts]

I sold a rotisserie motor kit to a buyer. Before he purchased it he asked me for some measurements which I supplied. He paid for the item and shipping and I shipped it.

Now he messages me and says that the bracket wasn't in the box and that the rod doesn't fit on his barbecue. I realized that I forgot to pack the bracket so I though ill ship that separately but  He want's me to pay return shipping and give a full refund. What do I do in this case? 

The package is heavy so it will be expensive. Am I supposed to pay or him?

[momcqueen]

You will have to pay return shipping because the buyer has received an Item that is Not as Described.

Offer to send him what you forgot in the first place but if he is soured on the whole idea here, there's not much you can do but take the lump and agree to receive it back at your own expense. You will have to refund the buyer the whole amount he paid for this, item plus shipping. This means you're out of pocket for postage both ways. 

Better luck next time. It gets easier as you gain more experience selling. The first few times I had to pack an order and print a label with an international customs declarations and the works, I thought my head was going to explode. It didn't.