AWS Schema Conversion Tool - Troubleshooting a Connection Error?

I have a security / permission / connection problem using SCT.

I'm using SCT locally to migrate my SQL Server DB to an Aurora DB in AWS. I get a "Connection wasn't established. Check connection properties." error. The log file is no use, all it has is a caught Java exception and stack trace: "com.amazon.sct.dbloader.exceptions.DbLoaderHandledException".

I created the Aurora DB with public access.

In SCT my connection details are:

Server name: mobile-reports-instance-1.c9vuf469uzhv.us-east-1.rds.amazonaws.com

Port: 5432

Database: I tried both regional cluster, "mobile-reports-instance-1" and writer instance names: "mobile-reports"

Username: postgres

And the correct passsword.

How can I troubleshoot this? I have no information to go on. Do I need to add an internet gateway to my DB or is that done when I select "allow public access"?