Probably should wait for others to answer - but we built some of our own stuff to do something like this in 4c4. Basically just tracked the quantities available to purchase on contracts with suppliers. I am not even sure how it worked anymore - but I think it basically monitored GRP purchase orders and would release them automatically, create all the necessary paper work and interface records. Now that I typed it not sure if this is even relevant to your issue. So best to just wait for some other ln users.
My latest mantra - make sure you have latest stpapi patches and the latest session object. If on LN then please explore the option of using DAL2 functionality.
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