As mentioned above, the typical cause is the silicone washer, normally in the top inside of the lid, has fallen off and likely inside the water chamber. Retrieve, and return to the underside of the lid, that’s what fixed my problem and now no leaks.
You may also find a second smaller problem, as I did, where a portion of the silicone O-ring that sits at the base of the threads, just visible under the top plastic of the espresso machine, was pushed under the lid. This O-ring keeps excess water on the top of the espresso machine from going inside where the electrical components are at. Instructions here to address that problem: https://www.ifixit.com/Patrol/Guide/31913