Hi, I'm the author of RTK Query. Please do not use that kind of createRequest helper function. That is taken from a tutorial that grossly misunderstands what baseQuery is made for (and spreading to other tutorials now). Essentially, baseQuer y is already a createRequest function like this - the return value of an endpoint's query function will be passed as first argument into baseQuery , which will in the case of fetchBaseQuery then call fetch . So please use fetchBaseQuery correctly instead here: export const api = createApi({ baseQuery : fetchBaseQuery({ baseUrl, // either you can just set `headers` here: // headers: { "Accept": "application/vnd.api+json" } // or you use `prepareHeaders` where you can do some calulations and have access to stuff like `getState` or the endpoint name prepareHeaders : ( headers, { getState, endpoint, type, forced } ) => { headers.set( "Accept" , "application/vnd.api+json" ) return headers } }), endpoints : ( builder ) => ({ getSomeStuff : builder.query({ query : () => { url : `/someStuff` } // or the short notation: if you only have an `url` just pass a string // query: () => `/someStuff` }), }) }); I would greatly appreciate it if you could change that up in this tutorial as this is essentially a bad practice and we do not want it to spread.