Enhance `invdata` endpoint for Xero invoices

src/ZGoBackend.hs

@@ -643,9 +643,10 @@ routes pipe config = do
             if res
               then status ok200
               else status noContent204
-  get "/invdata" $ do
-    invReq <- jsonData
+  post "/invdata" $ do
+    invData <- jsonData
     xeroConfig <- liftAndCatchIO $ run findXero
+    let invReq = payload (invData :: Payload XeroInvoiceRequest)
     case cast' . Doc =<< xeroConfig of
       Nothing -> do
         status noContent204