Data Action Fails to Map Zendesk Ticket Fields to Genesys Cloud Attributes

What is the reason this setting causes the Genesys Cloud Data Action to return a 400 Bad Request when trying to push Zendesk ticket data into Genesys Cloud custom attributes?

We are migrating our ticketing logic from Zendesk to Genesys Cloud. In Zendesk, we used simple tag-based routing. Now, we are trying to use a Data Action in Architect to fetch ticket details via the Zendesk REST API and map them to Genesys Cloud interaction attributes. The Data Action configuration seems correct, but the execution fails every time.

The error log shows:

Error: Invalid attribute format. Cannot map field 'ticket.priority' to 'custom_attributes.z_priority'.

We are using Genesys Cloud Architect v5.0. The Zendesk API call succeeds (200 OK), but the mapping step crashes. Here is the payload configuration for the Data Action:

{
 "name": "Zendesk_Ticket_Fetch",
 "type": "http",
 "url": "https://company.zendesk.com/api/v2/tickets/{{interaction.ticket_id}}.json",
 "method": "GET",
 "headers": {
 "Authorization": "Basic {{secrets.zendesk_auth}}"
 },
 "mapping": {
 "output": {
 "z_priority": "body.ticket.priority",
 "z_subject": "body.ticket.subject"
 }
 }
}

Is there a specific syntax for mapping nested JSON objects from Zendesk to Genesys Cloud attributes? Or is this a limitation of the current Data Action version?