Do you realize that the pointy-paren in

  $data->()
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is a subroutine call ?

The subroutine call is completely different from yout hashref-dereference in

  $data->{somekey1}{somekey2}
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What you seem to be looking for (It is unclear from your description) is something like:

$y='{channel}{item}';

foreach my $e (@{eval("\$data->$y")}){...
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