Did you use the IRS non-filers website to register for the stimulus payment? If so then a 2019 tax return was effectively filed and you cannot e-file another 2019 tax return.
See this TurboTax support FAQ for how to proceed - https://ttlc.intuit.com/community/tax-topics/help/stimulus-how-to-file-your-return-after-getting-rej...
