GetToString() occasionally returns nothing

Hey, I made a recursive function to do that and it seems to work fine. Here is the code I used : 

'*****************************************************************************************
' GetContent
'*****************************************************************************************
sub GetContent()
    ' request the content feed from the API
    xfer = CreateObject("roURLTransfer")
    xfer.SetCertificatesFile("common:/certs/ca-bundle.crt")
    xfer.InitClientCertificates()
    port = CreateObject("roMessagePort")
    xfer.SetMessagePort(port)

    xfer.SetURL("https://myvalidurl.com/page?parameter=sample")

    data = TryToGetData(xfer, port, 5)
    if data <> invalid and data <> ""
        ProcessContent(data)
    else
        m.top.error++
    end if

end sub

'*****************************************************************************************
' TryToGetData
'*****************************************************************************************
function TryToGetData(xfer, port, numberOfTries)

    if numberOfTries < 0 
        return invalid
    end if

    if xfer.AsyncGetToString()
        rsp = wait(10000, port)
        print type(rsp)
        if type(rsp) = "roUrlEvent"
            
            code = rsp.GetResponseCode()
            print "Response code is " code

            if code <> 200
                print "Re-trying to load content"
                triesRemaining = numberOfTries - 1
                return TryToGetData(xfer, port, triesRemaining)
            else
                print "Content retrieved correctly"
                return rsp.GetString()
            end if

        end if
    end if
    ' Should never get here
    return invalid
end function