Outbound Dialing: 400 Bad Request on Predictive Campaign Create - Zendesk Ticket ID Mapping Issue

Hi everyone! I am currently helping a client migrate their digital support stack from Zendesk to Genesys Cloud. In Zendesk, we used to rely on simple keyword matching for our chat bots, which was straightforward, but now I am diving into the outbound capabilities in GC and I am absolutely thrilled about the potential! However, I have hit a bit of a wall with the Outbound Dialing API during our migration testing.

We are trying to map old Zendesk ticket IDs to new Genesys interactions for our outbound campaigns. In Zendesk, we just attached a custom field with the ticket number, but in GC, I am trying to use the Campaigns API to create a predictive campaign and include contact data via the contacts array. When I send a POST request to /api/v2/campaigns/predictive, I get a 400 Bad Request error with the message: Invalid contact data format. The 'external_id' field is required and must be unique.

I am using the Genesys Cloud Python SDK version 1.6.0. My environment is EU1. I have ensured that every contact object in my payload has a unique external_id corresponding to the Zendesk ticket ID, but it still fails. In Zendesk, duplicate ticket IDs were impossible by design, so I assumed uniqueness was guaranteed. Is there a specific format required for the external_id in the outbound context that differs from the Zendesk integration? I want to make sure I am not missing a configuration step in the Admin Console under Outbound settings. Any practical migration advice on how to structure this payload correctly would be amazing!

I have seen this 400 error often in my load testing environments. It is usually not a syntax error but a validation issue with the payload structure. The Outbound API is strict about the ticket_id field. If you are migrating from Zendesk, you must ensure the ID is passed as a string, not an integer. Also, check if the Zendesk integration is fully configured in Admin.

Here is a working JSON payload for the POST /api/v2/outbound/campaigns endpoint:

{
 "name": "Zendesk Migration Campaign",
 "description": "Testing ticket mapping",
 "campaignType": "predictive",
 "enabled": false,
 "dialing": {
 "maxContactsPerDay": 100,
 "maxAttempts": 3
 },
 "contactList": {
 "id": "your-contact-list-id"
 },
 "server": {
 "id": "your-server-id"
 },
 "wrapUpCode": "your-wrap-up-code-id",
 "customContext": {
 "source": "zendesk",
 "ticketId": "123456789" 
 }
}

In my JMeter tests, I use a JSON Extractor to pull the contactListId and serverId from previous API calls. This avoids hardcoding IDs. Also, remember the API rate limits. If you are creating many campaigns, add a delay between requests. I use a constant timer in JMeter with 1000ms delay. This helps avoid 429 errors.

Check the error message carefully. It will tell you which field is invalid. Often, it is the customContext object. Make sure it is a valid JSON object. If you still have issues, share the full error body. I can help you debug the payload structure. My experience shows that most 400 errors in this API are due to missing required fields or wrong data types.