Preview runway site before DNS switch

We have uploaded all files for a runway site, migrated database, updated the config file etc. onto the live server and want to preview it to make sure everything is loading okay before switching the DNS to point at the live site.

However we're getting a 404 error. The url we are using is the ip address followed by the c-panel username, eg: https://123.456.789/~mysite

Could this be because we are using this temporary URL?

We looked on the server error logs and it says "URL to redirect is missing"?

Thanks