The documentation notes that:
Mandatory information.
For invoices to Spanish users. You MUST have entered a NIF for the client this is a requirement from AEAT. The only exception would be if no NIF is available to use the clients Passport Number in the Client’s ID Number field. AEAT requires the census data on the recipient. Sending will fail if you attempt to send an invoice to a client without these details.
That is true for invoices, but in B2C sales one might also need a Factura simplificada (simplified invoice / “ticket”) instead of a full invoice. It would be strange to ask a customer for their ID Number if they go shop for a 5 euro/month subscription for example.
Will support for factura simplificada in Verifactu be added? Without this B2C businesses who have to use verifactu basically can not use invoiceninja to my understanding.
Best regards
Daniel