Node.js req.flash issues

I'm having issues in returning messages with req.flash()
I'm trying to return a string message to the view instead it's flashing 1.
This is the short code:
return res.render('index', {
error_msg: req.flash('error_msg', 'Not found'),
success_msg: ''
})

Start with the req.flash() call shown in the issue and compare how messages are added with how they are retrieved before res.render(). Confirm what value the view receives and define done as rendering the requested flash message rather than the numeric value shown in the report.

Written by the indexing model from the issue text.