G'day ObiPanda,

From your description, I think you're after something like this:

$ perl -e '
    use Data::Dump;

    my @Subscription = (
         {
         Sub_Name               => "Morph",
         Archive_File           => "Morph Archive.txt",
         },
         {
         Sub_Name               => "Analogue",
         Archive_File           => "Analogue Archive.txt",
         },
         {
         Sub_Name               => "Cat",
         Archive_File           => "Cat Archive.txt",
         },
         {
         Sub_Name               => "Zoonotic",
         Archive_File           => "Zoonotic Archive.txt",
         },
         {
         Sub_Name               => "Hydro",
         Archive_File           => "Hydro Archive.txt",
         },
    );

    some_sub([map +{Sub_Name => $_->{Sub_Name}}, @Subscription]);

    sub some_sub {
        my ($single_scalar) = @_;
        dd $single_scalar;
        return;
    }
'
[
  { Sub_Name => "Morph" },
  { Sub_Name => "Analogue" },
  { Sub_Name => "Cat" },
  { Sub_Name => "Zoonotic" },
  { Sub_Name => "Hydro" },
]
[download]

Breaking that down into more manageable chunks:

• In some_sub(...), the ... represents what you "send ... to a subroutine".
• What you're sending is [...]. That's an arrayref and covers "preferably by reference". Here, the ... represents the contents of the arrayref.
• The arrayref contents are generated using map. You'll note that there are two forms: map BLOCK LIST and map EXPR,LIST. The second is used here but, as the EXPR is a hashref ({...}), the leading '{' can be confused with the leading '{' of a BLOCK. Adding a plus, "map +{...", removes that confusion — this is described in more detail about two-thirds of the way down the map page (look for the paragraph beginning with "{ starts both hash references and blocks ...").
• The hashref EXPR is a key/value pair. The key is Sub_Name; the value is $_->{Sub_Name}; your OP code suggests you understand this — ask if that's not the case. The LIST is @Subscription.
• In sub some_sub {...}, I've used dd, from Data::Dump, to show that a single scalar is received which is an arrayref with "one key & value per array/hash" as you put it.