Why do I get an error submission if I haven’t submitted? Duplicative social security
If you used the non filer portal to register for the stimulus payment, you efiled a tax return with $0 income. Now you will have to print and mail your "real" return to get it accepted. Write "Amended Return" across the top of the federal form 1040 before you mail it.
The non filer portal was to be used only by persons not filing a tax return.