In a previous post I asked about the 503 service unavailable issue but got no response. Meanwhile I found out that the issue is caused by the connection to the postgresql database not working. I am running a Ubuntu 20.04 server administered by Webmin. Webmin and Ubuntu tell me that there is no postgresql database installed. When I run openproject reconfigure with the option to install a local postgresql server I get the message: INFO: existing installation found. Skipping to next step.
                                           INFO: Checking connection to PostgreSQL server... psql: error: connection to server at "127.0.0.1",                                                port 45432 failed: Connection refused
                                           Is the server running on that host and accepting TCP/IP connections?

Purging the postgresql server fails with the message that it's not installed. Synaptic tells me that none of the postgresql packages are installed. How can I fix this?