{ "properties": { "associatedcompanyid": 123456 (ID from created company above), "firstname": "John", "lastname": "Doe", "jobtitle": "Founder", "email": "john@zappos.com" } }
3. Hubspot will correctly associate the contact with the company you specified in "associatedcompanyid", but will also create a secondary empty company that's not associated with any contact (shouldn't)
Hubspot will always create a "zappos.com" company based on the contact's email even if you just want to associate with the "zappos-corp.com" company you created.
These additional domains will be used for checking during contact creation. The field you want to update is called "hs_additional_domains". I believe this is a list, so set the company domain to zappos.com and maybe additional domain to zappos-corp.com (or vice versa if that makes sense to you). If the company has the correct domains, you shouldn't need the associatecomapnyid proerty defined.