RE : PostgreSQL logical incremental backup for version 9.6 and above

I've a requirement to backup incremental data from PostgreSQL database server which are hosted as 'database as a service' like 'Amazon RDS' , Azure Database etc. 

Full dump can be taken using pg_dump. But is there is a way to capture incremental changes to the database ?  I read about logical replication slots which can be created for each database to capture incremental changes. 

But how do we know from where we should backup the SQL statements (as we need need skip those statements already backed up by pg_dump). 

I thinking of following steps. 

Step 1: Create logical replication slot

Step 2: Run pg_dump ( for full load ). 

Step 3: Capture the changes since last pg_dump using replication slot - How to know this information ?

Thanks in advance for any advise. 

Thanks

Girish