@{$self->_getGood()}

If $self->_getGood returns an array (or, indeed, a list) then there's no need to dereference it again.

I assume that '6' is the first item in the returned list.

my $files_to_send = map {"$stage/$_.pdf"} $self->_getGood();
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But as you hint that you already know, you shouldn't be assigning that to a scalar, so you probably want:

my $files_to_send = [ map {"$stage/$_.pdf"} $self->_getGood() ];
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