fix: check before request

CORS preflight channel did not succeed
https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSPreflightDidNotSucceed

Answer used
corydolphin/flask-cors#292 (comment)

backend/matcha/__init__.py

@@ -1,4 +1,4 @@
-from flask import Flask
+from flask import Flask, request, jsonify
 from flask_socketio import SocketIO
 from flask_cors import CORS
 from os import environ
@@ -42,4 +42,14 @@ def create_app():
 
     socketio.on_namespace(MainNamespace("/"))
 
+    @app.before_request
+    def before_request():
+        headers = {
+            "Access-Control-Allow-Origin": "*",
+            "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS",
+            "Access-Control-Allow-Headers": "Content-Type",
+        }
+        if request.method.lower() == "options":
+            return jsonify(headers), 200
+
     return app