DMS endpoint connection test fails for Postgres 13, DMS 3.5.2

The error you're encountering with your AWS Database Migration Service (DMS) endpoint connection test for PostgreSQL 13 using DMS engine 3.5.2 appears to be related to a prepared statement issue. This type of error can occur due to various reasons, but there are a few steps you can take to troubleshoot and potentially resolve the issue:

1. First, ensure that your source and target database configurations are correct. Double-check the endpoint details, including the host name, port number, and database name.

2. Verify that the security groups and network access control lists (NACLs) are properly configured to allow traffic between the DMS replication instance and your PostgreSQL database.

3. Check that the user credentials used for the DMS task have the necessary permissions to access the database and perform the required operations.

4. If you're using a custom database name in your connection string, try using the default database name "postgres" instead. Sometimes, connection issues can occur when the specified database doesn't exist.

5. Ensure that your PostgreSQL instance is accessible and that there are no ongoing network or hardware issues affecting its availability.

6. Consider updating to the latest version of the AWS DMS engine, as newer versions often include bug fixes and improvements that might address this type of issue.

7. If the problem persists, you may need to enable logical replication on both the source and target databases, as this is sometimes required for CDC (Change Data Capture) connectivity in homogeneous migrations.

If none of these steps resolve the issue, it's recommended to contact AWS Support for further assistance, as they can provide more specific guidance based on your exact configuration and setup.
Sources
Troubleshooting for RDS Proxy - Amazon Aurora
AWS DMS homogenous migration from PostgreSQL to Amazon Aurora PostgreSQL | AWS Database Blog
Troubleshooting connections to your RDS for PostgreSQL instance - Amazon Relational Database Service

I Have upgraded DMS engine to 3.5.4 but still getting the same when testing the source database end point