PC win 8.1 delete everything how?

I'm trying to delete my laptop so that I can sell it, but this is not possible because I get this error message.

Create a Windows 10 stick and install Windows 10 on it.

Your data will also be deleted!

In addition, it can then be sold better.

Can you write me a cover letter which laptop that is, maybe I'm interested!

A laptop still with 8.1? How much do you want to pay 20 Euro? That should be 10+ years old.

So what? I just like these laptops. I would even buy some with Windows 7!

I sent you a friend request

No, I only had one stick in win 8.1