I assume you are filing MFS. Try entering all 9's or 999-99-9998. Not sure if it will work in newer programs (did work years ago) You could also apply for an ITIN, and wait (you have plenty of time for 2024 taxes) or just mail it in

Unfortunately, all 9's did not work.

If I remember correctly, you can enter NRA and the IRS will accept it.  You would ignore the error that ProSeries is giving and you may need to disable error-checking (you need to e-file from Homebase to do disable error-checking).

I have not actually done it, but I've read others who have said that works.