Session field is None

I have hosted a rest API written in Flask in one domain and my react app in another domain. I can successfully log into the system using a username and password. However, when I try to hit an endpoint, I get None for the username attribute (locally everything is working without any issues).

def login_required( f ):
    def wrap( *args, **kwargs ):
        project_owner = session.get( 'username' )
        if project_owner is None:            
            logging.error( ERROR_MSG.LOGIN_ERROR_MSG )
            return response.cannot_process_redirect( ERROR_MSG.LOGIN_ERROR_MSG, '/' )
            return f( *args, **kwargs )
    return wrap

I think I have applied the correct CORS policies but I cannot get it to work. Applied CORS configurations are as below.

app.config['CORS_HEADERS'] = 'Content-Type'
app.config['SESSION_COOKIE_HTTPONLY'] = False
CORS( app, supports_credentials = True, resources = {r"/api/*": {"origins": ""}} )

And the fetch request of the endpoint looks like below.

export function getUsers() {
    const url = 'users/'
    const requestOptions = {
      method: 'GET',
      credentials: 'include'
    return ( dispatch ) => {
    return fetchReq( requestOptions, url ).then( ([response, json]) => {
        // Do something
    } )

If I use Postman, I can use endpoints without any issues. One thing I noticed is in my request and response session value strings are different. Below is a screenshot of request-response headers. Any ideas?
Request-Response Headers

Source: React Router Questions