Is there a way to delete specific timeline events? I can create or update existing ones, but what if I have to delete mistaken events?
It’s not currently possible to delete timeline events. In general, testing the Timeline Events API should be done in a test portal to avoid creating test/junk events. That said, I can totally understand the use case for being able to delete events. If you have the inclination, I would encourage you to check out the Ideas Forum on the HubSpot Community. There, you can post/vote on ideas for the product so your use case can be seen by HubSpotters, partners, and other customers alike.