🌎 Immigrant founders: 83(b) without ITIN or SSN?

Hello fellow immigrant founders! If you have a startup but don't have an ITIN or SSN, how did you go back submitting the 83(b) election form? Are you still eligible for that?

Background: I started my startup back in 2017 when my cofounder was still in Hong Kong. He submitted the 83(b) within 30 days as requested, but the IRS is saying there is no record of it now, most likely because he didn't have an ITIN or SSN. Now he's worried he'll be taxed a lot more. Just curious how people went about this.

Thank you!