Unable to file due to "filing incomplete" and "whoops, we hit a snag loading your data"...

I completed all my relevant forms, and there are no errors at the review. I don't owe any taxes, so I just need to pay by credit card (for this Turbotax online service) and complete the e-filing of my federal return (I don't live in the USA at all, so I think I don't have a US state filing). However, I am unable to do so. I have never had a problem in several past years using TurboTax.

The error only says, "whoops, we hit a snag loading your data"... and at the top of the page it says, "filling incomplete". But I cannot find anything incomplete. I checked and rechecked. I cleared the browser's cache and cookies. I tried again with a different browser, then on a different device. No luck. Finally, I reset my return and redid everything from scratch. I still get the same error.  I am unable to complete my payment and efiling becaue of this error.