This part worked to send the variable, so much so that in the web browser I see it being sent.
chatflowConfig: { vars: { apiKey: "TEST_KEY" }
However, I cannot receive it in the Flowise stream. According to JanR, it would be possible to receive it via prompt from the agent, which I was unable to do.
Could someone, especially JanR, show in the flow how they received the variable?