Error 500 after importing posts from WordPress

I try to install ghost via Heroku and Netlify as described here Create a free JAMStack blog using Ghost, Heroku and Netlify | by Zing Zai | Medium

However after importing Wordpress posts via .json file - my ghost homepage shows 500 error ER_USER_LIMIT_REACHED

I have around 200 posts.

Try to go to https://onlinehikes.herokuapp.com/ to reproduce.

I can’t access Ghost dashboard at the moment.