AshGraphql provides two JSON types that may be used. They are the same except for how the type is serialized in responses.
:json_string- serializes the json to a string, e.g"{\"foo\":1}":json- leaves the json as an object, e.g{foo: 1}
By default, :json_string is used. The configuration for this is (uncharacteristically) placed in application config, for example:
config :ash_graphql, :json_type, :json