FullStack Developer for bug Fixing

I have a web application with chatbot feature, frontend is in react.js and backend is in Flask API's. I am getting some API's errors mainly (503 Service unavailable and CORS) on APIs. Also the frontend seems to be working. Here is the link to application : [login to view URL] Senario is user gets 5 random questions and given the 4 options to each. On each answer pren-type score is calculated on basis of that it selects the winner. At conclusion page openAI assistant call has been made to get the result for the winner. I am looking for a FullStack developer with invaluable knowledge in React and Flask to fix these issues mentioned below : 1 - Multiple user / concurrency issue is very repeatable. Just do 3 sessions at the same time and at least one will fail. Front end logs in browser shows this clearly. This is most important. 2 - Wrong preben leaderboard podium image in tie scenarios (eg. 2 preben types have a score of 2). Image selection must use the same rule as winner selection 3 - ESLINT issues. To be looked at needs to be fixed. Looking forward to get the experienced developer to fix these issue. Thanks