Do I need to provide the IRS both the husband’s and wife’s SSN (if I seller-financed a home to a married couple) … or just one of their SSN’s?

I owner-financed a home to a married couple in 2017.  As of now, I only have the husband's SSN.  When I fill out the "Seller-Financed Mortgage Interest Statement", must I fill in both SSNs ... or will just the husband's SSN be acceptable to the IRS?  Thanks!