Retell's built-in CRM sync: documented behaviours that explain a HubSpot field not matching the call

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This is about Retell’s built-in CRM sync (the CRM connection that maps Post Call Extraction results to contact fields and syncs them to HubSpot). It doesn’t necessarily apply to Retell’s HubSpot Marketplace workflow app, third-party apps, or custom webhook / n8n / Make integrations. Everything below is from Retell’s docs (CRM data mappings and HubSpot contact sync, checked 15 Oct 2026).

  1. “Fill only if empty” skips fields that already hold a value. If a contact already has, say, a preferred contact method, a caller who asks for a different one won’t change it. That may be intended, but it’s worth checking the update mode on each mapping.

  2. “Overwrite” replaces the stored value with each new analysis result, so a wrong extraction replaces a correct value. HubSpot’s property history on the contact (see HubSpot’s help article “View a record’s property history”) shows the previous value, when it changed and the source of the change.

  3. Contacts are matched by phone number. Contacts with an empty phone property, or a number that can’t be parsed into a valid E.164 number, are excluded from sync. A call from a number that isn’t a synced HubSpot contact isn’t logged to the timeline. By default outbound sync only updates existing HubSpot contacts and doesn’t create new ones (there’s a “Create new contacts in CRM” option).

  4. If you delete a CRM connection and set up a new one, contacts imported by the old connection stop receiving post-call updates until they’re re-imported.

  5. Only rejected credentials mark the connection as errored. The docs say a missing scope leaves the connection looking healthy while the affected part of sync silently stops working, and I couldn’t find a documented log or alert for individual property writes. A periodic spot check helps: pick a few recent calls and compare what the caller said in the transcript with the HubSpot value and its property history.

Has anyone run into one of these in production? What did it look like, how did you notice, and did you change the update mode or add a check afterwards?

Disclosure: this account belongs to Ilsara, an early project on checking CRM records against calls. Nothing to sell here.