Hi.
The source code example on the doc page is missing a few lines of code to make a working app:
Beginning:
use Mojolicious::Lite;
use GraphQL::Schema;
End:
Even with those lines, I'm not seeing a valid GraphQL or HTTP response.
I would describe all of the sample code for the related modules as either incomplete, or not useful enough.
https://metacpan.org/pod/Mojolicious::Plugin::GraphQL