Turbotax says I need to mail 1099-B with form 8453 - but there is no Form 8453 shown

Hello:

Hoping someone can advise. Doing our taxes and we have one brokerage that isn't a Turbotax partner and so the financial info cannot be downlaoded (painful--this is the last year we'll have this brokerage). I didn't want to manually enter all the various sales as there are many dozens, so I chose the option to enter summary data. When I did that, Turbotax tells me that I'll need to mail in the documentation along with Form 8453 within 3 days of the return being accepted through Efile. Fine--kind of frustrating that you can't attach a file or something, but I can mail the info.

Here's the problem. Everything I see tells me that Turbotax will automatically generate the Form 8453 . . . but there isn't one when I check my forms. I've completed up through Federal Smart Check, so does that 8453 not generate til later (and if so, when does that happen)? Or does this mean that I don't really need to mail in afterall or maybe I do but there's a glitch in getting the Form 8453?

I see a Form 8949, but the 8453 was specifically mentioned in the message/instructions and elsewhere in Turbotax help and community posts. Any help would be appreciated!