Waveapps GraphQL schema dump throws error

I'm trying to use php-graphql-oqm against Waveapp GraphQL.
https://developer.waveapps.com/hc/en-us/articles/360018937431-API-Playground
It's free to register.

I'm getting an error from php vendor/bin/generate_schema_objects:
Inline argument of type String is not allowed. Provide data using GraphQL variables.

Any idea what might be happening? 
