G'day ptone,

Welcome to the Monastery.

Building upon what ++hippo pointed out, consider using qq for your outermost quotes.

You're currently producing JSON like this:

$ perl -E 'my $x = "YZ"; say q{{"X":"$x"}}'
{"X":"$x"}
[download]

I expect you want JSON more like this:

$ perl -E 'my $x = "YZ"; say qq{{"X":"$x"}}'
{"X":"YZ"}
[download]