I have an 8332 form to fill out, due to the father of my son and I not being together, but the issue is that he doesn’t have a valid US SSN. What am I supposed to do?

I haven’t filed yet due to me needing the 8332 form, but one issue I am facing is that the father doesn’t have a valid SSN  for me to put on the form since he isn’t a US citizen. How am I suppose to fill out this form since he can’t file taxes legally.