is already routed to the Default zone of another application. Remove that mapping or use a different URL.

This problem has been occuring to me when I was trying to restore a web application from a backup. I had the website created already, and deleted it, so it wasn’t just the content database that was restored.
That is what caused this error: Deleting a web application and trying to recreate it.
It will remember the Alternate Access Mappings (AAM), so we will just work around it.
My backup was used to transfer the web applications from another farm. Basically cloning the production server to a staging server (oh the troubles that has given me…), but I will go through that another day.

The answer to how to fix this error is to go to central Administration -> “Operations” -> Alternate Access Mappings (under Global Configuration).

My bet is you will have the “offending url” in the list. Click it and change it to something else. Add “Blabla” to the end of it.

Create the website now (or in my case do the restore from backup).
Once the creating of the site is done, go back to the AAM page and change the url back to whatever it was before.