You have a problem.
Since it is an SFP order then Amazon will not cover an INR claim unless you shipped with signature confirmation.

And of course you do not know who did receive the order since the only thing you have is an address.
I am afraid that you are just gong to be stuck taking this loss yourself.
I know this is not what you want to hear.

Buy Shipping covers SFP that are marked delivered. That changed this fall.

My response to the buyer would be that it was delivered on Friday to the address you provided. They should contact that address to retrieve their package.

As @JwsMarket stated, the SFP policy changed and no longer requires signature confirmation – just must use Amazon Buy Shipping. (We don’t do SFP but I knew I had seen that change, but was not sure to post it here until I saw someone else also reference that change from earlier this year.)

If the shipping was purchased through Amazon’s Buy Shipping, you’ll be okay. The customer may open an A-Z, just respond with tracking, the fact it shows delivered, and that label was purchased via Amazon Buy Shipping - You’ll be covered.

Keep the A-Z response short and sweet, bullet points if at all possible. A-Z workers don’t have much time to make judgements, so make response clear, concise and easy on the eyes.

Coppied & Pasted From
https://sellercentral.amazon.com/gp/help/help.html?itemID=CRVNRBZBVGBK543&language=en_US&ref=ag_CRVNRBZBVGBK543_relt_1781

If you purchase Amazon Buy Shipping and ship on time, you are protected against claims where a customer reports problems with delivery. Amazon will cover the cost of these claims and they will not affect your ODR.

Here is a lovely technicality of Amazon.
We are required to only ship to the address as provided. If the customer entered the wrong address we are not responsible.

However if we didn’t use signature confirmation then as far as Amazon is concerned it doesn’t matter that the customer had it shipped to the wrong address.
It’s a customer is 100% at fault but Amazon don’t care.

I recently had this happen and I was reluctant to cover the replacement simply because of the way the customer was approaching it. I contacted Seller Support and this is what they said:

"In this case, I would like to inform you that as this is not your mistake, no need further action from your end.

In case, the buyer files A to Z claim or Chargeback for this order, an email notification will be sent to you by our internal team informing the same, you may reply back to that email in detailed explanation of the situation so that they look into it and do the needful.

If the buyer posts a negative feedback, I request you to request a feedback removal using the feedback removal manager or you can also contact providing the order so that we will investigate and assist you further."

The next morning I swallowed my pride and refunded the customer anyway.

UPS offers $100 basic insurance for each package and must be requested by the shipper… Since you bought through Amazon, I’m not sure who is the shipper?

Sorry for all the misguided information the other sellers are giving you. Even if you purchased the shipping on Amazon if the customer does INR you will loose. I had 2 of these last week and appealed both only to loose. Its a buyers market on Amazon

I had this problem last week. Sent an email to buyer but no response. Mailed an insured package thru usps and sent buy another email. Again no response. If the package disappears with delivery to the address, will my purchases insurance cover?

I have had this happed many many times before.

You purchased the label via amazon buy shipping - you are covered.

The mistake is that of the buyer.

How would you know the address is incorrect, unless you were advised of such PRIOR to the package being shipped.

You did what amazon will advise you was the correct thing to do - (you shipped to the address provided on the order form)

As another poster has already stated, the buyer had ample time to correct the issue before the item was actually shipped.