Recording sales in my POS system from dispatched orders

[Isobel1]

I need to integrate my existing POS system with Shopify. I have a company supporting the data api that will communicate item details and stock for 5 stores refreshing every hour. 

I need a solution for when an order is set to dispatched/complete on Shopify it sends the transaction to my POS provider. I also want in store pick up. 

My existing system sends a pick up order to a local till, when set to ready to collect a customer is emailed, on collection the sale goes through on our POS sales record. 

We can’t have sales recorded on Shopify and not on our POS system for proper sales recordings. 

I would consider Shopify POS only for ease of in store pick up but I still 100% need the sales sent to our legacy POS system.