Hi Irene,
I was able to login to your web hosting control panel and I see that you’re using PHP v7.2.8 which is a good sign. However I see that your PHP memory limit is set to 256MB and PHP max script execution time is set to 30 seconds and I do not see a way to increase them within your control panel.
Then when I have tried to connect to your server through FTP, I’m getting the following error in secure note. Which seems that you may have enabled IP based restriction. You may need to contact your hosting provider with regard to that.
Some hosting provider do not allow to increase PHP memory limit manually. If have tried @paul.r’s recommendations above, then you need to contact your hosting provider and ask them to increase for you.
Basically ask them to increase your PHP memory limit to 512MB and also ask them to increase PHP max execution time to 120 or above value.
You can confirm those changes by head over to WordPress Dashboard -> WP Serverinfo section. Then try testing your Cornerstone editor and see if that helps.
Thanks!