Hello,
I think there is a problem right now with your cloud authentication API (https://preview.keenthemes.com/metronic8/laravel/api/login).
The field api_token is null in the response body. It is then impossible to validate the token with the second API call (https://preview.keenthemes.com/metronic8/laravel/api/verify_token).
The React demo versions on your site also seem to be impacted by this problem.
Best regards,
Florian