On my Local server everything was good was using mailtrap mail server as smtp server. but when my website is on live server and when I trying to reset password (forgot password ) getting following error screenshot is attached.I am using hostgators cpanels inbuilt smtp. any more details I will provide if needed.
You need to install PHP version 7.1 because nullable types were introduced in 7.1:
?string $value
And from the Laravel docs:
You will need to make sure your server meets the following requirements:
PHP >= 7.1.3