OK... it seems to be saving now. The only thing I did differently was to not use auto-fill, and to include my country code on the phone number, starting with a +. According to this link... https://developer.apple.com/documentation/appstoreconnectapi/interpreting_and_handling_errors/parsing_the_error_response_code ...the 409 error implies improperly formatted data. So I tried to fiddle with the entry a bit and it seems to have worked. Share if this works for you! :)

It's definitely not special characters. All I am doing is trying to switch the "sign-in required" toggle - no text entered. If I open the log in Chrome I see the following error... logLevel: "ERROR" message: "API Response Error: SAVEAPPREVIEWDETAILSRESPONSE" stackTrace: "status code: 409 --- api correlation key: LAXXXXXXXXXXXXXXXXXXXXXE" (Where the XXX = a number - don't know if I should share it or not!) Is there anything weird we might have in common? For example, I have two App Store Connect accounts on my apple ID.

Me too - exact same thing. How am I supposed to submit my app?