The installation failed

There’s a good chance your postgres database is damaged. Open the logs and if you see lines similar to below, you have a postgres database issue.

 database system was interrupted record with zero length invalid primary checkpoint record 

You will find the log here:

 /Library/Logs/PostgreSQL/PostgreSQL.log 

The Roundcube installer needs a healthy database.
Repair Postgres and try the Roundcube installer again.