@Geoffrey Montel
Thank you for your post!
As of right now, using the Log Analytics’ REST API to manage watchlists, you can only create, modify, and delete watchlists and their items using the REST API - Manage watchlists in Azure Sentinel using REST API. If you'd like the ability to administer Azure Sentinel Watchlists using REST APIs, I'd recommend leveraging the Azure Sentinel GitHub repo to create a feature request for our engineering team.
Additional Links:
Azure Sentinel REST APIs
Azure Sentinel Tech Community
If you have any other questions, please let me know.
Thank you for your time and patience throughout this issue.
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