This applies only to organizations in Mexico: every line item on a CFDI 4.0 needs a Product/Service Key and a Unit Key from the SAT catalogs.

Which key Cord uses today

Cord doesn’t yet have a product catalog with its own SAT key per item: when stamping, every invoice line is sent with the generic key 01010101 (“Not in the catalog”) and unit H87 (“Piece”). Those are valid keys with the SAT and won’t block stamping, but they don’t describe your specific line of business — if your accountant needs a more precise key (for example, 43231500 for business software, or E48 for a service unit), you’ll need to correct it manually on the resulting CFDI or ask your accountant to adjust it from their own system.