Get your taxes done using TurboTax

Check to make sure you have entered the K-1 for that LLC into TurboTax.  If so, review your entries into TurboTax to make sure you entered the Section 199A information that came with the box 20 code V Statement or STMT (box 17 code V if the LLC is taxed as an S Corp).  You must Continue after that box 20 code V screen to enter the 199A Statement/STMT amounts for the applicable lines on the two screens at the bottom of this post.

If you've done that, you may need to look at the K-1 for that LLC, the QBI Component form linked to that K-1, and the QBI Ded Summary form to understand "what happened" to your QBI deduction calculation.  You can do that in the Forms mode of the Download/CD version of TurboTax, or by creating a PDF of all the forms in your TurboTax Online return.