It appears it is not possible to add a company contact, unless that contact has an email address - The api assumes that a contact is a customer that needs to login, and thus wont allow creating a contact without an email address, which I dont think is a valid assumption. We should be able to add a contact to a company without an email address for that contact.
Topic summary
API limitation: adding a company contact requires an email address because the API treats contacts as customers who must log in.
Impact: companies cannot create non-login contacts (e.g., internal or vendor contacts) without emails, which is seen as an invalid assumption for business needs.
Request/Outcome: a feature change is requested to allow creating company contacts without an email. No workaround or resolution is provided; discussion remains open.