Connecting RDS to an external server for replication issues

Hi all, We're going to be moving to AWS soon, and I am wanting to setup replication to an external main server . I have followed this guide: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Procedural.Importing.External.Repl.html

Steps I took: Made a user on the Main server mocking what was in the write-up

I flushed privileges'

I then set the main server on our AWS database CALL mysql.rds_set_external server ('XX.XX.XX.XX', 3528, 'repl_user', 'MYSQL_PASSWORD_Main', 'mysql-bin-changelog.008401', 14545731, 0);

I am presented with the errors below. The MySQL port is not 3528 and not the default 3306 and although I set it differently it seems its trying to connect to that port still. Just a note we have this server replicating to another dedicated server as well so replication is working on the machine.

2021-12-13 18:30:00 2889 [Note] Error reading relay log event: SQL thread was killed

2021-12-13 18:30:00 2889 [Note] SQL thread exiting, replication stopped in log 'mysql-bin-changelog.008386' at position 53651981 2021-12-13 18:30:00 2889 [Note] was XX.XX.XX.XX:3306

2021-12-13 18:30:00 2888 [ERROR] I/O: error connecting to 'repl_user@XX.XX.XX.XX:3306' - retry-time: 60 maximum-retries: 86400 message: Can't connect to server on 'XX.XX.XX.XX' (4 "Interrupted system call"), Internal MariaDB error code: 2003

2021-12-13 18:30:00 2888 [Note] I/O thread killed while connecting to

2021-12-13 18:30:00 2888 [Note] I/O thread exiting, read up to log 'mysql-bin-changelog.008386', position 53651981

2021-12-13 18:30:00 2888 [Note] was XX.XX.XX.XX:3306 ----------------------- END OF LOG ----------------------

Any other things someone could suggest please?