Redis [QUESTION] [ERR] The source node should not be a cluster node.

i want migrate redis 2.8.19 standalone to redis cluster 6.2.4 using follow command:

redis-cli -a 'xxx' --cluster import 172.2.16.3:6379 --cluster-from 172.2.16.56:6399 --cluster-from-pass 'xxx' --cluster-copy --cluster-replace

but it throw: [ERR] The source node should not be a cluster node.

what's wrong with it？ does mean source node is a cluster node？but 172.2.16.56:6399 is a standalone