What is the correct way to handle Ticket-to-Interaction mapping via API during Zendesk migration?

Background

We are currently in the final stages of migrating our support operations from Zendesk to Genesys Cloud. As a migration specialist, I am focused on preserving historical context by mapping old Zendesk ticket IDs to new Genesys Cloud interactions. The goal is to ensure that when an agent pulls up a conversation, they can see the legacy Zendesk reference number for continuity. We are using the Genesys Cloud Platform API (REST) directly, as the SDK documentation seems less robust for this specific custom attribute mapping.

Issue

When attempting to update an existing interaction’s custom attributes via the PATCH /api/v2/interactions/{id} endpoint, the request fails with a 400 Bad Request. The payload includes a custom attribute key zendesk_ticket_id with a string value. The error response indicates:

{
 "errors": [{
 "title": "Bad Request",
 "detail": "Invalid property 'customAttributes' for interaction type 'task'."
 }]
}

In Zendesk, adding custom fields is straightforward via their ticket API. However, Genesys Cloud appears to have strict schema validation for interaction types. We are using the standard task interaction type for these migrated records. I suspect the issue might be related to how custom attributes are defined in the Architect or if they need to be pre-provisioned as specific custom definition entities before they can be attached to an interaction via the API.

Troubleshooting

1. Verified that the custom attribute zendesk_ticket_id is defined in the Genesys Cloud admin console under Custom Attributes.
2. Confirmed the API token has the interaction:view and interaction:update permissions.
3. Tested with a minimal payload excluding other fields, but the 400 error persists specifically when customAttributes is included.
4. Checked the API documentation version (v2), but it is unclear if task interactions support dynamic custom attributes without a prior definition schema match.

Is there a specific sequence required to map these attributes, or should we be using a different endpoint like PATCH /api/v2/customattributes? Any guidance on aligning Zendesk’s flexible field structure with Genesys Cloud’s stricter interaction model would be appreciated.

The problem is that Genesys Cloud does not natively support a direct foreign key relationship between external ticketing systems like Zendesk and internal interaction objects, which means relying on simple ID mapping will fail during data retrieval. Instead, the correct architectural pattern for AppFoundry partners involves leveraging the Interaction’s custom_attributes field or, more robustly, utilizing the integration_id and external_id properties within the Interaction API payload to establish a bidirectional link. When migrating historical data, you should execute a batch update using the PUT /api/v2/interactions/{interactionId} endpoint, ensuring you include the legacy Zendesk ticket ID in the custom_attributes array under a key like zendesk_ticket_id. For real-time continuity, your AppFoundry integration should listen for the interaction.created or interaction.updated webhooks, parse the payload to extract any existing external references, and then query your Zendesk instance to fetch the legacy ticket details, injecting them into the agent desktop via a Premium App UI. This approach avoids the pitfalls of trying to store massive JSON blobs in the interaction object itself, which can lead to payload size errors and slower API responses. Additionally, ensure your OAuth tokens have the interaction:view and integration:edit scopes, as missing permissions are a common cause of silent failures during bulk updates. If you are dealing with high-volume migrations, implement exponential backoff for your API calls to respect the platform’s rate limits, especially since bulk operations can easily trigger 429 errors if not properly throttled. This method ensures that agents can see the historical context without compromising the performance of the core interaction engine.

Have you tried leveraging Data Actions to push the external_id directly into ServiceNow upon interaction creation? The suggestion above is accurate, but mapping requires explicit payload configuration. Ensure the custom_attributes in Genesys Cloud align with the ServiceNow REST API schema to preserve the Zendesk reference during migration.