pty

1 2	kali -t tmux attach -t <target_session_name>

or:

1 2	kali -o RequestTTY=no tmux attach -t <target_session_name>

situation:

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3

$ ssh 192.0.2.125 tmux attach
open terminal failed: not a terminal

The solution is to simply force pseudo-terminal allocation.

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$ ssh -t 192.0.2.125 tmux attach
[...]

Define RequestTTY in OpenSSH SSH client configuration file to make this permanent.

$ cat ~/.ssh/config
Host 192.0.2.125
RequestTTY yes