AWS RDS mysql.rds_set_external_master remains disabled after setting autocommit to 1

The goal is to create a master-master replication consisting of two RDS MySQL 5.6 instances, db0 and db1. I orientate myself by this article.

So far, I have created db1 as a read-replica of db0 and set read_only = 0 and autocommit = 1 at db1's parameter group.

To set a replication master manually, AWS defined the mysql.rds_set_external_master() function. According to AWS's documentation on this function, it is disabled by default and can be enabled by setting autocommit to 1.

Meanwhile, about 45 minutes have passed and the instance has been rebooted twice and excuting call mysql.rds_set_external_master() still returns RDS_SET_EXTERNAL_MASTER is disabled on this host and does not update the master.

Any help with this is highly appreciated.