Give permission to Python Flask application running on Apache2 ubuntu

I'm running a Flask application on Apache2 server on Ubuntu. The application would take input from a form and save it to a text file. The file exists only for the moment when it's uploaded to S3. After that it's deleted.:

            foodforthought = request.form['txtfield']
        with open("filetos3.txt", "w") as file:
            file.write(foodforthought)
        file.close()
        s3.Bucket("bucketname").upload_file(Filename = "filetos3.txt", Key = usr+"-"+str(datetime.now()))
        os.remove("filetos3.txt")

but the app doesn't have permission to create the file:

[Errno 13] Permission denied: 'filetos3.txt'

I already tried to give permissions to the folder where the app is located with:

 sudo chmod -R 777 /var/www/webApp/webApp

but it doesn't work

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