Open purchase orders

Hello Experts

We are going live with EDI in couple of weeks time and now struck with the query to retrieve the open purchase orders.

The process is we send the purchase orders to Tradex HUB and the hub accepts only those invocies which are against the open valid purchase orders. In the HUB they do not have the provision to store the header and line status hence we came up with a workaround to concatenate PO header and line status. We wrote the below query but it is not retrieving the right results. Can you please look into the below and let me know if there is any thing wrong