Exception: 

Validation error of type FieldUndefined

"message": "Validation error of type FieldUndefined: Field...."

Resolution:

Validation error of type FieldUndefined Salesforce GraphQL API Exception occurs when the running user doesn’t have access to the requested resources. For example, if you are querying Lead records and if the running user doesn’t have Lead object access. To fix this issue, Lead Object access should be given to the running/integration user.