You can't upload a form 8949 that was generated externally.
Instead choose the mail in option.
You summarize what is on the 8949 on one line (or 2 if Long Term and Short Term holding periods).
Then TurboTax will present the mailing address where you send the transaction details (your Form 8949) to the IRS within three business days of IRS accepting your e-Filed tax return.
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