Tying to connect to docdb with ssm AWS-StartPortForwardingSessionToRemoteHost

I am trying to connect to docdb cluster from my local laptop, using ssm port forwarding. I did the following

aws ssm start-session --target instance-id \
--document-name "AWS-StartPortForwardingSessionToRemoteHost" \
--parameters "host=clusterhost,localPortNumber=27017,portNumber=27017

But when I try to connect, it gives me back Server selection timed out after 30000 ms message back. I have created the bastionbox with cdk, and have attached AmazonSSMManagedInstanceCore role to it Connecting from bastion box to docdb works however, so I guess there is some issue with port forward by ssm. Is there a way to debug this and find the root cause?