Error Heroku Deployment of Flask app: gunicorn.errors.HaltServer: <HaltServer 'Worker failed to boot.'4>

I’m using heroku to deploy my multiple app but this keeps popping , H10 error app crashes. and error 503, how can I solve it ? .Itried everything over the internet and heroku dev help docs but nothing seems to work for me. I think my app takes alot of time to load thats why its crashing there a solution tothis?
my procfiles:
web: gunicorn index:server --preload --timeout 300 -b:8000