This is where the GET is located

CatsDataSource.kt

class CatsDataSource(retrofit: Retrofit) {

    private val api: CatsApi = retrofit.create(CatsApi::class.java)

    fun getNumberOfRandomCats(limit: Int, category_ids: Int?) =
        api.getNumberOfRandomCats(limit, category_ids)

    interface CatsApi {

        @GET("images/search")
        fun getNumberOfRandomCats(@Query("limit") limit: Int, @Query("category_ids") category_ids: Int?): Single<List<NetCat>>
    }
}