When the HubSpot CRM originally launched, contacts could only be associated with a single company. This association was done using the associatedcompanyid, since only a single association from a contact to a single company was supported. Since then, we've added new objects, such as tickets and products, and also added support for parent and child companies. These new objects, and the new relationships between these objects, have required several updates to the systems that are used to manage those associations.
As part of those updates, we want to make sure that all associations in the HubSpot Sales and Service Hubs are managed through a single system: the CRM Associations API. The CRM Associations API allows you to manage associations for all objects across the HubSpot Sales and Service Hubs. Ths API also supports creating associations in batches, including creating multiple types of associations in the same batch, compared to the individual endpoints for making associations for specific objects one at a time.
Beginning on April 26, 2019, the associatedcompanyid property will become read-only, meaning that the property can no longer be set or updated when creating or updating contact records. At that point, you will need to use the CRM Associations API to make any associations between contacts and companies.
Please let us know if you have any questions by replying to the forum post here.