The ‘BT Nested FlowScript’ and ‘FSM FlowScript State’, is meant to be used so that you can have a flowscript as an internal part of the root graph (be it an BT or FSM), and not meant as a way to control an existing ‘FlowScript Controller’ with it.
If you want to Start/Pause/Stop an existing ‘FlowScript Controller’, you can use the action called “Control Graph Owner”, which can be found under the “Utility” category.
Alternatively, if you want to for example send an event to that ‘FlowScript Controller’, you can use the action “Utility/Send Event”.
In both cases, you can select the target ‘FlowScript Controller’ by overriding the action’s target with the checkbox and assigning the FlowScript Controller component reference:
Please let me know if these work for you, or if you are trying to achieve something different.