How can you set up the idProperty to use a unique parameter, such as an email address, other than the contact record’s ID number?

The idProperty query parameter tells HubSpot which unique property should be used to identify the record. For contacts, email can be used instead of the contact record ID when the request supports alternate identifiers. This is useful when an integration stores email addresses but not HubSpot record IDs. The parameter keeps the API call targeted to the correct contact without requiring a separate lookup first. The property used must be unique enough for reliable record identification.