Error message": "getting node from external cluster [RC_Test] failed" between nodes on 2 docker hosts

Elastic Stack Elasticsearch
11 
- network.host=0.0.0.0
- transport.host=0.0.0.0
- network.publish_host=<SERVER_IP>

Can you try setting these settings.

Remote Cluster Settings: On the cluster that connects to this node, make sure to use the host IP:
cluster.remote.RC.seeds: ["192.168.70.129:9300"]