The Replication feature does not use the REST API, but instead uses Postgres’ logical replication. To support it, you must ensure that
- Each region has a different region number
- Postgres’ port (5432) is exposed
To set it up, in the screen you mentioned, give the hostname, port (should be 5432), and database credentials of the remote Postgres database (or the database appliance if you are running Postgres in an appliance).