Solved. The token must be passed as data in the query (was in the documentation)
From the document https://zoneminder.readthedocs.io/en/stable/api.html
Login using API 2.0 token (OK)
then
The following command functions as intended
curl -k -XGET https://server/zm/api/events/index/MonitorId:1.json?token=...token... (OK returns data as expected)
but if I add pagination, it fails with "401" not authenticated
curl -k -XGET https://server/zm/api/events/index/MonitorId:1.json?page=1?token=...token... (ERROR 401)
The document doesn't show how to add token and pagination. I wonder what I am doing wrong or missing?