This is part of the "Deferral for Certain Schedule H or SE Filers Smart Worksheet"
As posted by another member, the answer is to remove 0 and enter no value. This clears the error.
Yes, you are correct. Leaving this field completely blank is an option. The system can update with leaving this field blank. As always, it can be useful to close out of your program and close the browser window completely. Re-open in Chrome.
If you are still experiencing unexpected results, there is another workaround.
You can recalculate the deferral by temporarily recalculating this section by adding more income. Otherwise, without any adjustments, you may not get back to the same screens.
To return to the interview section to adjust these entries and un-trigger any deferral that you no longer want, follow these steps:
Enter a temporary amount as income in the self-employment section that will result in you not having a refund.
Decline to defer any self-employment tax.
Remove the temporary income.
For more details, see TurboTax Expert @DawnC's answer here, about 2/3 down the page: Resolve Sch SE-T Max Deferral Line 18 must be entered.