Thanks, the .%Get("pdf",,"stream<base64") works.

It is super frustrating though.
This produces an error: <PARAMETER> 127 %GetNext^%Iterator.Array.1
 

Set iter = jsonob.value.labReports.%GetIterator()
While iter.%GetNext(.key,.labReport,.type) {
    w !,"type: "_type
}

I do not know if it a bug on my side or the documentation:

My code:

try{
  Set jsonob = ##class(%DynamicObject).%FromJSON(httprequest.HttpResponse.Data)
  w !,"statusCodes: "_jsonob.%Get("statusCode"),!
  Set iter = jsonob.value.labReports.%GetIterator()
  While iter.%GetNext(.key, .labReport) {
  w !,"reportName: "_labReport.%Get("reportName")
  Set pdf=labReport.%Get("pdf",,"stream<base64")
  w !,"pdf: "_pdf.Read(20),!
  }
} catch(tException) {		
  w !,tException.DisplayString(),!
}

JSON looks like this( pdf the offending big string):

Output:

statusCodes: 200

reportName: Long-Oeloff-Badenhorst.pdf
<MAXSTRING> 5 ztestpdf+36^Test.Testy.1

ztestpdf+36 = Set pdf=labReport.%Get("pdf",,"stream<base64")

Good info!
What happens if the particular task takes longer than a minute and the busines sservice is invoked again?