Why am I required to mail in form 8543 along with my 8949?

[drice78]

After submitting my filing electronically, TurboTax (desktop) informed me a few screens later that I need to mail in form 8543 with the reason that I selected to not include my 8949 forms electronically. I do not select to not include them, so something is broken here. 

Of note I could imagine others will not look past the initial notification that my information has been sent off and stop using the app, missing this critical step (if really needed). 

If these forms are needed and TurboTax already has them completed for me, then they should also be printed with the 8543, not just 8543. Another opportunity for someone to not complete this step correctly. 

[Mike9241]

Turbotax is saying you marked a line on form 8949 with code M which indicates it consists of multiple trades. The IRS wants details of those trades. attaching a  pdf of 1099-B to your e-filed return is not possible so you must send it to the IRS using form 8453 

[fanfare]

IRS requires details of your SELL transactions to be supplied on some Form 8949,
or on your other forms (e.g. consolidated 1099-B or spreadsheet) which have the same information and in the same manner as Form 8949.

Either way, if you choose to summarize only, you have to mail the transaction details to the IRS within three business days of IRS accepting your e-Filed tax return. (unless you have attached a PDF of the transactions details to your e-Filed return. TurboTax Online will ask for it).

This is the "Mail-in option".

Detail Reporting Exception: if you summarize Category A or Category D, Form 8949 is not needed for transactions without adjustments. No mailing is necessary.

The exception does not apply to wash sales, since they have an adjustment.

Form 8453 is just a coversheet that identifies your situations that require mailing of paperwork.

[fanfare]

"I do not select to not include them, so something is broken here. "

The form 8949 you e-filed is a summary 8949, not a detail 8949.

@drice78