I am not able to add participants to certain activities

[r2d2]

Hi,
Did you see an error message while trying to perform the operation? If so, can you share the details?

Reporting REST API issues

If you stumble across an issue that you observe with the REST APIs, please make sure you provide the following details: Describe the issue (if possible, with the scenario, logs, screenshots) How does it affect your use case? Which endpoint is causing the issue? What is the payload structure* ? What is the mode of authentication (API token / OAuth)*? What is the response code and error message that you get? What is the value of the x-correlation-id response header that you received? …

The participant information can be passed as an array of objects to updateActivity endpoint

https://developers.pipedrive.com/docs/api/v1/Activities#updateActivity