How do I separate sessions between app users in Twilio using Flask sessions?

During testing of my app with ngrok, two of my users texted the Twilio number at the same time and they some how landed in the same session so any counters I was using got messed up for their own respective user experiences. How can I ensure that each user texting the number to use the app will have their own separate experience? Is the trick to somehow create a dynamic SECRET_KEY in Flask session?

Some code below

from flask import Flask, request, session
from twilio.twiml.messaging_response import MessagingResponse

SECRET_KEY = 'a secret key'
app = Flask(__name__)

@app.route("/sms", methods=['GET','POST'])
def sms_logic():
        # Increment the counter
        counter = session.get('counter',0)

        # Initiate conversation + Save the new counter value in the session
        body = request.values.get('Body', None)
        counter += 1
        session['counter'] = counter

        # start our TwiML response
        resp = MessagingResponse()

        if counter == 1 and body.lower() == 'target_string':

            resp.message('response 1')

        elif counter == 1 and body.lower() != 'target_string':

            resp.message('Unknown entry. Please try again.')


            resp.message('response 2 ')

    except Exception as e:


if __name__ == "__main__":

I am clearing the session to reset the counter instead of waiting 4 hours for the session to expire especially if the user would like to go through the app again to make another entry.

Thanks in advance!