Im getting this error on your example

[codeitlikemiley]

{"data":null,"errors":[{"message":"Field 'createPost' argument 'title' of type 'String!' is required but not provided. (line 2, column 3):\n  createPost(description: $description, imageUrl: $imageUrl) {\n  ^","locations":[{"line":2,"column":3}]}]}

Seems like the example is not updated yet

[codeitlikemiley]

manage to resolve this by adding title in all related files that is missing itt