I can't figure out why my session variables aren't transferring to other flask routes. I believe I have it set up properly, but I'm having a problem with this code: from flask import Flask, request, jsonify, redirect, url_for, render_template, session from flask_session import Session import requests import os import json app = Flask(__name__) app.secret_key = os.urandom(24) # Session setup SESSION_TYPE = 'filesystem' app.config.from_object(__name__) Session(app) @app.route('/') def index(): shop_origin = session.get('shop_origin', 'Shop Origin In Session Not Set') print("index shop_origin is equal to: %s" % shop_origin, flush=True) if not shop_origin: session['have_shop_info_in_session'] = False if 'have_shop_info_in_session' in session: print("have_shop_info_in_session is equal to: %s" % session['have_shop_info_in_session'], flush=True) if 'have_shop_info_in_session' in session and session['have_shop_info_in_session']: shop_info = session.get('shop_info', 'No Shop Info Found') return render_template('app_interface.html') else: return render_template('fetch_shop_info.html') @app.route('/set_shop_info', methods=['POST']) def set_shop_info(): data = request.get_json() shop_origin = data.get('shopOrigin') if not shop_origin: return jsonify({'error': 'Shop origin not provided'}), 400 session['shop_origin'] = shop_origin print("Loaded session shop_origin: %s" % session.get('shop_origin'), flush=True) session['have_shop_info_in_session'] = True # Set the flag to true print("set_shop_info have_shop_info_in_session is equal to: %s" % session['have_shop_info_in_session'], flush=True) return jsonify({'status': 'success'}), 200 When this code runs, I get positive flags in the logs with Loaded session shop_origin: testing-store.myshopify.com and set_shop_info have_shop_info_in_session is equal to: True, but as soon as the Javascript from the fetch_shop_info.html redirects to the index flask route, the logs show index shop_origin is equal to: Shop Origin In Session Not Set. Why is the variable not transferring to the other route in the session? Cookies are enabled in the browser. EDIT: I tried running the code in a different browser and it seems to work fine, so the problem has to be my browser (Brave Browser). I have Brave Shields turned off for Shopify and I can see that the cookie SEEMS to be stored correctly by the browser. I'm still not sure what the problem is exactly but I'm a little bit closer to figuring out what it is.