We are attempting to update contacts via the email property rather than ID using a private app connection on Contacts API v3.
We can successfully make the call with the actual contact ID, but receive an error when attempting with email.
The CRM API Docs say: "The idProperty query parameter doesn't appear on the Endpoints tab due to technical limitations, but it can be used for contacts exclusively with email. To use an email address as the unique identifier, set the idProperty as email and enter the email address in place of the contact ID. This should be set as a query parameter rather than added to the request body."
The bearer token/private app is verified to be working properly when making calls because I tested it before trying this specific action.