Is it asking you to mail the 8949 itself, or mail a statement / 1099-B?
Did you input this non-covered sale as part of a 'summary' or 'one by one' in the 1099-B section. For sales that need adjustments (e.g. wash sales) or fall into these non-covered categories if you just input it as summaries then it will tell you to mail the detail. If you input it as "one by one" with all the details of the investment (dates etc) then you shouldn't need to mail anything. This may require putting separate 1099-B's in for the same broker - one as a summary for all the covered items (usually most of it), one at the detailed level for the exceptions (usually only a few sales/lots).
That's been my experience in the past with TT Desktop and I input my 1099's manually I do not import and then make sure it's not telling me to mail anything. Not sure about TT Online or new requirements/features/bugs for 2024. Hope this helps.
