How to call callOpenAI function

app.js

app.post("/plan", function(req, res) {
    let occasion = req.body.occasion;
    let pax = req.body.pax;
    let budget = req.body.budget;
    let theme = req.body.theme;
    let country = req.body.theme

    const prompt = `Teach me how to plan for ${occasion}, for ${pax} people. I have a budget of ${budget} dollars. My theme is ${theme}. I am in ${country}.`
    callOpenAI(prompt).then(response => {
      console.log("Response", response)
      res.json(response)
    }).catch(error => {
      console.log("ERROR", error)
    })
});