I’m not really comfortable sending Valve (let alone any company) a picture of my DL to verify my payment. They said that, alternatively, I could send a picture of an “official document” that has my name and address on it. Does that mean I can send them a piece of mail instead?
Seems you have triggered their fraud prevention AI, for whatever reason.
You could upload the photo of your DL after blacking out any data they don’t already have on you anyway. A mail will not do → “official” document.