AFAIK PostGres is not a supported DB for MicroFocus yet? Where in your installation guide is PostGres mentioned?

ScanCentral DAST does support PostgreSQL; however, WebInspect does not. Here are the database types supported by SC DAST:

• SQLServer

• PostgreSQL

• AzureSQLServer

• AzurePostgreSQL

• AmazonRdsSQLServer

• AmazonRdsPostgreSQL

For ScanCentral DAST, you would simply define the database type (provider) in the DatabaseSettings section of the settings file (YAML or JSON file) - https://www.microfocus.com/documentation/fortify-ScanCentral-DAST/2210/SC_DAST_Help_22.1.0/index.htm#DynCLI/DynCLI_Database.htm?TocPath=Configuring%2520the%2520ScanCentral%2520DAST%2520Environment%257CCreating%2520and%2520Using%2520a%2520Settings%2520File%257C_____1

Here is a snippet from one of my configuration files where I've defined AzureSQLServer:

Instead of AzureSQLServer you would enter the appropriate database provider.

Keep in mind that you will need to have already created the DBO account and database before running the ScanCentral DAST Configuration utility.