Where to store some important data fetched from API so that I can use it in multiple routes?

I am developing OTP authentication. So here my routes in express -

const express = require("express");
const router = require("express").Router();
const rp = require("request-response");

router.post("/sendOTP", (req, res) => {

const { mobile_number }  = req.body; // receive the mobile number

const otp = randomize("0000"); // generated 4 digit otp

options = {
     method: "GET", 
     url: "xxxxx/xxxxx/xxxxx/${otp}",   // calling my otp service provider to send otp to my user
}

rp(options).then((response)=>{

       // response.details contains the unique otp session id which I have to use in another route where I am verifying otp
}).catch((err) => console.log(err));
});

router.post("/getOTP", (req, res) => {

// user will put otp he received from his mobile

const { otp }  = req.body; // receive the otp

options = {
     method: "GET", 
     url: "xxxxx/xxxxx/xxxxx/${otp}/${otp_session_id}",   // calling my otp service provider with otp and session id of otp
}

rp(options).then((response)=>{
        console.log(response) // otp verified.

}).catch((err) => console.log(err));
});

this is simple code. Now my problem is - how can I store that otp_session_id so that I can use it in two routes sendOTP and getOTP ? I used cookieParser, cookieSession, expressSession, nothing worked out. please any simple steps / solutions will be great.

thanks :)