Dataflow Timeout and "Query Contrains Errors"

Hey, I've set up a new gateway to access our data through an api / Gateway and want to set it up as a dataflow. 

I'm using a query which works in powerbi desktop , it takes about 10-15 minutes to refresh for 43k lines, but when I try to validate the query when setting up the dataflow it says. "The operation is timed out" and "The query contains errors". I have also tried pulling only 4k lines of data and get the same problem. 

Any help would be really appreciated

let
Source = Json.Document(Web.Contents("https://jira.corp.company.com/rest/api/2/search?jql=JIRAQUERY")),
BaseUrl = "https://jira.corp.company.com/rest/api/2/search?jql=JIRAQUERY",
EntitiesPerPage = 1000,
GetJson = (Url) =>
let RawData = Web.Contents(Url),
Json = Json.Document(RawData)
in Json,
GetTotalEntities = () =>
let Json = GetJson(BaseUrl),
Total = Json[total]
in Total,
GetPage = (Index) =>
let Skip = "startAt=" & Text.From(Index * EntitiesPerPage),
Url = BaseUrl & "&" & Skip & "&maxResults=" & Text.From(EntitiesPerPage),
Json = GetJson(Url),
Value = Json[issues]
in Value,
GetUrl = (Index) =>
let Skip = "startAt=" & Text.From(Index * EntitiesPerPage),
Url = BaseUrl & "&" & Skip & "&maxResults=" & Text.From(EntitiesPerPage)
in Url,
EntityCount = List.Max({ EntitiesPerPage, GetTotalEntities() }),
PageCount = Number.RoundUp(EntityCount / EntitiesPerPage),
PageIndices = { 0 .. PageCount - 1 },
URLs = List.Transform(PageIndices, each GetUrl(_)),
Pages = List.Transform(PageIndices, each GetPage(_)),
Entities = List.Union(Pages),
#"Converted to Table" = Table.FromList(Entities, Splitter.SplitByNothing(), null, null, ExtraValues.Error)
in
#"Converted to Table"