Several QuickBooks Online APIs - including Custom Fields, Projects, and Sales Tax - utilize GraphQL. GraphQL is an API query language that simplifies client-side requests.
Using GraphQL, apps can do a lot of work with just a single query, such as query multiple resources and entities, request data in a specific format, or get the server to perform several operations. With GraphQL, all queries go to a single endpoint on the server. The server parses queries and returns only the requested data in the requested format.
For information about how to fix GraphQL errors, see Fix GraphQL errors.