Full Stack Application with React, Node, Stripe, Sendgrid

A time ago I did a front-end application to get weather data from the city you introduce in a search box.

I carried on with that application to converted it in a full stack app.
Basically in this app, apart of getting weather data, you can login if you have a google account.Once logged in, you can buy credits at one dollar per credit and with those credits you can create a Survey made out of a title , the subject, a body and the recipient where you can place all the emails you want to direct to.
You can check a list of all the emails you sent.

This one has been a lot of more of work. I followed the course of Full Stack Application of Stephen Grider in Udemy and use Stripe and Sendgrid services.
If for the fron-end part I worked freely on my own design, for the back end part I didn’t departe to much from the course as still no too confident.

I didn’t try logging in but just as some quick feedback I get undefined values in the title for the weather location and if I go to /weather (or just refresh the /weather page) it just gets stuck and does not redirect.

Not really much feedback I know, I just wanted to let you know what I found.

Yes, thanks for the feedback.
Those issues are regarding the front-end part of app, I will try to sort them.
but I would like some feedback about the back-end

Thank you again.