return rejected

[Flinders]

Extension filed & accepted 7/15/20, went to file return and I get this message: "Submission must not be a duplicate of a previously accepted submission." How do I fix it?

[Just-Lisa-Now-]

A return has already been filed for the SSN/EIN. 

Did the client use the Non Filer site to get the stimulus?

[dkh]

Did you verify you checked the "First Extension Ready to EF"  e-filing and not accidentally efiled the return?