Access denied for user in DMS instance

Question

I am trying to set up a data replication task with AWS DMS (MySQL to MySQL).

The endpoint configurations have been successfully tested but the task is not terminated because it gives the following error:

Last Error Task error notification received from subtask 0, thread 0 [reptask / replicationtask.c: 2673] [1020414] Error 1045 (access denied for user '[origin_db_user]' @ '[replica_instance_ip]' (using password: YES)) connecting to MySQL server '[origin_db_host]';

How do I grant access to the replica instance?