well, you have to do nothing.

Are you able to connect from the source to the target machine manually with ssh? ensure that you check it as the same user as the one that runs the script.

Oh, I see what the problem is:

%args={port => $portnumber ,host =>$host ,user => $username ,debug => 
+1};
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is wrong, you have to write it as

%args=(port => $portnumber ,host =>$host ,user => $username ,debug => 
+1);
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using (...) instead of {...}

BTW, you would have already noticed it if you were using

use strict;
use warnings;
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on your code!!!!!!!!!