SQL Server 2016 Replication using RMO

We are using SQL Server replication using RMO. We have SQL 2016 (Standard Edition) on the server acting as the publisher and SQL Server Express Edition as the subscriber.
Previously, the distributor and the publisher were on the same server and the replication was working.
We have a client application, the data needs to be synced with the server on a regular basis.
We have Transactional and merger replication set and rely on pull approach where the client application pulls the data on demand.
For security reasons, the client doesn't want to expose port 1433 (or any other port) on the publisher to the subscribers.
So, we decided to move the distributor on a remote server, so that the subscriber talks to the publisher via remote distributor. (The remote distributor can connect and talk to the Publisher.) However, I am getting an error...