Outbound Campaign API 429 Rate Limiting on Contact List Imports

Need some help troubleshooting unexpected 429 Too Many Requests errors when importing large contact lists via the Outbound API.

We are deploying a high-volume dialer integration through AppFoundry and hitting rate limits on POST /api/v2/outbound/contacts during batch imports. The service account has the outbound:contact:write permission and we are using the standard OAuth2 flow for multi-org access. Despite spacing requests at 100ms intervals, the gateway returns 429 responses after approximately 500 records. The error payload indicates a burst limit violation rather than a sustained rate limit. Is there a specific burst allowance for contact imports in the outbound module, or should we be implementing a different pagination strategy for bulk operations? Our current implementation uses the platform API v2 endpoints directly without the SDK abstraction layer.