F150 Lease Buyout Question

New to this forum and looking to learn a lot. I initially have this question.
My lease end date on an F150 is August 15th. I just made my last lease payment and my intent all along has been to purchase the truck. I’ll be on vacation when my lease ends so decided to do the deal now. Went to the dealer I leased from and worked a deal, signed a bill of sale, financed thru my credit union and delivered the dealer the check. I think its all done, but here’s where it takes a turn.
Did the deal Friday 7/3, delivered a check Tuesday 7/7. I get a call from my salesman today saying they sold me the vehicle at too low of a price. He said the deal should have been for the residual value of the vehicle and proceeds to text me a picture of a new bill of sale. The new bill of sale shows a purchase price of $36,015.79, which he said is the residual of the vehicle.
The original bill of sale that the dealer produced, was signed by all parties and my bank wrote the check off of was for a vehicle value of $26,265.79
The dealership is now saying that we need to do a new deal because its off by almost $10k.

This was leased through FMC and FMC says to work with the dealer if you intend to purchase, so I did. Anyone have any experience or insight with this? Is my bill of sale final or am I on the hook for the difference between the purchase and the residual?

What was the residual value on your lease contract?

Yes it was.

I believe you misread my question.

Yes I did. The word “what” in front of the question totally changes how I read it lol.
I pulled the lease paperwork and it says $35,873.60

Seems like the dealer made a mistake. If you choose not to cover the difference then they will most likely just void the contract. So you aren’t “on the hook” but unfortunately it’s unlikely you will get your truck for $10K less then the RV. More likely, you will need to return your truck and the then buy another pre-owned one.

With such a big gap between market value and residual value, it means you had a pretty good lease that seriously outperformed the actual depreciation.