in reply to Unable to execute the get method from app.psgi file for Dancer2 app.

my $id = route_parameters->get('site_id'); redirect client(params->{$id})->authorize;

You are storing the value of the site_id param in $id. Then you are for some reason not using that variable, but fetching the value again ... but the second time you are looking for a parameter with the same name as the value.

The way forward always starts with a minimal test.