Conversational Agents - passing session parameters flow -> playbook not work

I am seeing the same issue reported in this thread (Topic 179637): Conversational Agents - passing session parameters flow -> playbook stopped working?

My route transition from a Flow to a Playbook works, but there is no context passed from the flow to the playbook (context is null).

The solution in that topic was to request access to the “private preview of input and output parameters.”

Is this feature now Generally Available (GA), or do we still need to request access to get parameter passing?