We were using a third-party application(mailgun) to signup the user. Mailgun sends the link to the mail of the user and when the user clicks the link on mail then the user will be sign in. But mailgun was providing this service to only one user. There it's written that it is applicable upto 5 users but the code was not running well. We tried a lot and in the end we get to know that we need a premium version of mailgun plus the proper domain name and hosting by GoDaddy. In the end we drop the idea of mailgun and uses the local verification tool i.e. bcryptjs.