The error message you are seeing on the wash sale entries is a result of automatic rounding.  If the wash sale adjustment is $0.49 or less, then it is automatically rounded to zero.  This type of rounding is allowed by the IRS. 

Unfortunately, zero is not a valid value for this field for TurboTax, thus the error message.

To enter a disallowed Wash sale:​​​​​​​

Income & Expenses

1. Scroll to Stocks, Mutual Funds, Bonds, Other
2. Answer Yes to Did you sell stocks, mutual funds, bonds, or other investments in 2020?
3. On the OK, what type of investments did you sell? screen, select Stock, Bonds, Mutual Funds. Then select Continue.
4. From here, you can import or manually enter your 1099-B.
5. Answer the questions about your sales. Choose to Enter sales one by one when asked.
6. On the Now, we'll enter one sale on your 1099-B screen, enter your info.
7. Check I have other boxes on my 1099-B to enter and enter the disallowed wash sale loss in box 1g.
8. Select Continue and answer any follow-up questions.

Note: You'll need TurboTax Premier, TurboTax Live Premier, or TurboTax Self-Employed, TurboTax Live Self-Employed, to add any 1099-B forms.

I received the reply but later went on to work on state taxes and when I finished and looked at review again, the message was that everything was ready to submit even though I had done nothing with the wash sale issue.  I've not had time to work on taxes since then but this is confusing to say the least.