That index was added in 5.1. I suspect that you had some preview version installed instead of the official 5.0. That would explain this.
Version 5.0 has been installed, and we don't have the preview version installed from other versions
Is there a way to fix the error?
The easiest option - restore the database backup and run service again. If you get the same error immediately on the first run - you didn't have the official version 5.0 originally.
I use MYSQL Database