seems similar to the bug https://github.com/NodeBB/NodeBB/issues/3489 so you may just need to update your dependencies (rm -rf node_modules && npm cache clean && npm i).
That worked, thanks!
I have selected the email verification option. user is successfully able to log in, but not receiving any verification mail. so no action can be done from the user side even if he logs in to account. Is it a problem of nodeBB version or any other mail configuration is required in the sandbox.
Have you set up an emailer yet?